Reference picture resampling in video processing

ABSTRACT

A method of visual media processing, including: determining, for a current video block, a motion vector for use in a sub-block based motion vector prediction (sbTMVP) process to locate a correspondingblock in a collocated picture for a conversionbetweenthe currentvideo block and a bitstream representation of the current video block, wherein the motion vector used in the sbTMVP process is computed in accordance with a scaling operation; and performing based on using the motion vector, the conversion between the current video block and the bitstream representation of the visual media data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/CN2020/116703, filed on Sep. 22, 2020, which claims the priorityto and benefit of International Patent Application No.PCT/CN2019/107159, filed on Sep. 22, 2019. The entire disclosure of theaforementioned applications is incorporated by reference as part of thedisclosure of this application.

TECHNICAL FIELD

This patent document relates to image and video coding and decodingtechniques, devices, and systems.

BACKGROUND

Digital video accounts for the largest bandwidth use on the internet andother digital communication networks. As the number of connected userdevices capable of receiving and displaying video increases, it isexpected that the bandwidth demand for digital video usage will continueto grow.

SUMMARY

The disclosed techniques may be used by video decoder or encoderembodiments during video decoding or encoding using alternative temporalmotion vector prediction.

In one example aspect, a video processing method is disclosed. Themethod includes determining, for a current video block, a motion vectorfor use in a sub-block based motion vector prediction (sbTMVP) processto locate a corresponding block in a collocated picture for a conversionbetween the current video block and a bitstream representation of thecurrent video block, wherein the motion vector used in the sbTMVPprocess is computed in accordance with a scaling operation; andperforming, based on using the motion vector, the conversion between thecurrent video block and the bitstream representation of the visual mediadata.

In another example aspect, another video processing method is disclosed.The method includes determining, for a current video block, a motionvector for use in a sub-block based temporal motion vector prediction(sbTMVP) process to locate a corresponding block in a collocated picturefor a conversion between the current video block and a bitstreamrepresentation ofthe currentvideoblock, whereinthe motion vector used inthe sbTMVP process is computed with respect to a center point of thecurrent video block; modifying the center point of the current videoblock by applying one or more operations; and performing, based on usingthe center point modified by applying the one or more operations, theconversion between the current video block and the bitstreamrepresentation of the visual media data.

In yet another example aspect, another video processing method isdisclosed. The method includes determining, for a current video block, amotion vector for use in a sub-block based temporal motion vectorprediction (sbTMVP) process to locate a corresponding block in acollocated picture for a conversion between the current video block anda bitstream representation ofthe currentvideoblock, whereinthe motionvector used in the sbTMVP process is computed with respect to a point inthe corresponding block in the collocated picture; modifyingthe point inthe correspondingblock in the collocated picture by applying one or moreoperations; and performing, based on usingthe point in thecorrespondingblockin the collocated picture modified by applying the oneor more operations, the conversion between the current video block andthe bitstream representation of the visual media data.

In yet another aspect, another method of video processing is disclosed.The method includes determining, for a conversion between a videopicture included in visual media data and a bitstream representation ofthe visual media data using sub-pictures, that a rule related to one ormore sub-pictures is satisfied by the conversion; and performingtheconversion according to the rule of constraint, wherein the rulespecifies that a size of a sub-picture in the video picture is aninteger multiple of a coding tree unit size associated with the videopicture.

In yet another example aspect, another method of video processing isdisclosed. The method includes determining, fora conversion between avideo picture included in visual media data and a bitstreamrepresentation of the visual media data using sub-pictures, that a rulerelated to one or more sub-pictures is satisfied by the conversion; andperforming the conversion according to the rule of constraint, whereinthe rule specifies that all sub-pictures in the video picture arenon-overlapping, and together the all sub-pictures in the video picturecover entirety of the video picture.

In yet another example aspect, another method of video processing isdisclosed. The method includes making a determination, for a conversionbetween a video unit of a visual media and a bitstream representation ofthe visual media data, whether a reference picture resampling (RPR)technique is used during the conversion; performing the conversion basedon the determination, wherein a flag corresponding to the determinationis included in the bitstream representation at a sequence parameter setlevel.

In yet another example aspect, another method of video processing isdisclosed. The method includes based on satisfying a condition,selecting an interpolation filter during a motion compensation processto derive a prediction block of a current block ofvisual mediadata,wherein the condition is based, at least in part, on determining that aresolution of a reference picture is different from a resolution of thecurrent picture and/or that a dimension of a window associated with thereference picture is different from a dimension of a window associatedwith the current picture; and performing a conversion between thecurrent block of visual media data and a bitstream representation of thecurrent block.

In yet another example aspect, another method of video processing isdisclosed. The method includes determining, for a conversion between acurrent block of a visual media data and a bitstream representation ofthe visual media data, that the current block is a combined intra andintra predicted (CIIP) block, wherein an intra prediction block for theCIIP block is generated using a size of a transform unit (TU), wherein,in the combined inter intra prediction (CIIP) block, a final predictionof the current block is based on a weighted sum of an inter predictionof the current block and an intra prediction of the current block; andperforming the conversion based on the determining.

In yet another example aspect, a video encoder apparatus is disclosed.The video encoder apparatus includes a processor that is configured toimplement a method described herein.

In yet another example aspect, a video decoder apparatus is disclosed.The video decoder apparatus includes a processor that is configured toimplement a method described herein.

In yet another aspect, a computer readable medium having code storedthereupon is disclosed. The code, when executed by a processor, causesthe processor to implement a method described in the present document.

These, and other, aspects are described in the present document.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 is an example of derivation process for merge candidates listconstruction.

FIG. 2 shows example positions of spatial merge candidates.

FIG. 3 shows an example of candidate pairs considered for redundancycheck of spatial merge candidates.

FIG. 4A-4B show example positions for the second PU of N×2N and 2N×Npartitions.

FIG. 5 is an example illustration of motion vector scaling for temporalmerge candidate.

FIG. 6 shows example candidate positions for temporal merge candidate,C0 and C1.

FIG. 7 shows an example of combined bi-predictive merge candidate.

FIG. 8 shows an example derivation process for motion vector predictioncandidates.

FIG. 9 is an example illustration of motion vector scaling for spatialmotion vector candidate.

FIG. 10 shows an example of alternative temporal motion vectorprediction (ATMVP) motion prediction for a CU.

FIG. 11 shows an example of one CU with four sub-blocks (A-D) and itsneighbouring blocks (ad).

FIG. 12 is a flowchart of an example of encoding with different MVprecision

FIG. 13A-13B show 135 degree partition type (splitting from top-leftcorner to bottom-right corner), and 45 degree splitting patterns. Anillustration of splitting a CU into two triangular prediction units (twosplitting patterns).

FIG. 14 shows an example of position of the neighboring blocks.

FIG. 15 shows examples of above and left blocks of a video block.

FIGS. 16A-16B show examples of 2 control point motion vectors (CPMVs)and 3 CPMVs.

FIG. 17 shows an example of affine MVF per sub-block.

FIGS. 18A-18B show examples of 4 and 6 parameter affine models.

FIG. 19 MVP for AF INTER for inherited affine candidates.

FIG. 20 shows an example of constructing affine motion predictors inAF_INTER.

FIG. 21A-21B show examples of control point motion vectors in affinecoding in AF_MERGE.

FIG. 22 shows examples of candidate positions for affine merge mode.

FIG. 23 shows an example of intra-picture block copy operation.

FIG. 24 shows an example of a valid corresponding region in thecollocated picture.

FIG. 25 shows an example flowchart for history based motion vectorprediction.

FIG. 26 shows modified merge list construction process.

FIG. 27 shows an example embodiment of the proposed valid region whenthe current block is inside a Basic Region.

FIG. 28 shows an example embodiment of a valid region when the currentblock is not inside a basic region.

FIG. 29 is a block diagram of an example of a video processingapparatus.

FIG. 30 is a flowchart for an example of a video processing method.

FIG. 31A shows an example of locations for identification of defaultmotion information in the current standards.

FIG. 31B shows an example of locations for identification of defaultmotion information in the proposed standards.

FIG. 32 is a block diagram of an example video processing system inwhich disclosed techniques may be implemented.

FIG. 33 is a flowchart for an example of a visual media processingmethod.

FIG. 34 is a flowchart for an example of a visual media processingmethod.

FIG. 35 is a flowchart for an example of a visual media processingmethod.

FIG. 36 is a flowchart for an example of a visual media processingmethod.

FIG. 37 is a flowchart for an example of a visual media processingmethod.

FIG. 38 is a flowchart for an example of a visual media processingmethod.

FIG. 39 is a flowchart for an example of a visual media processingmethod.

FIG. 40 is a flowchart for an example of a visual media processingmethod.

FIG. 41 is a block diagram that illustrates an example video codingsystem.

FIG. 42 is a block diagram that illustrates an encoder in accordancewith some embodiments of the present disclosure.

FIG. 43 is a block diagram that illustrates a decoder in accordance withsome embodiments of the present disclosure.

DETAILED DESCRIPTION

The present document provides various techniques that can be used by adecoder of video bitstreams to improve the quality of decompressed ordecoded digital video or images. Furthermore, a video encoder may alsoimplement these techniques during the process of encoding in order toreconstruct decoded frames used for further encoding.

Section headings are used in the present document for ease ofunderstanding and do not limit the embodiments and techniques to thecorresponding sections. As such, embodiments from one section can becombined with embodiments from other sections.

1. Summary

This patent document is related to video coding technologies.Specifically, it is related to motion vector coding in video coding. Itmay be applied to the existing video coding standard like HEVC, or thestandard (Versatile Video Coding) to be finalized. It may be alsoapplicable to future video coding standards or video codec.

2. Introductory Remarks

Video coding standards have evolved primarily through the development ofthe well-known ITU-T and ISO/IEC standards. The ITU-T produced H.261 andH.263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the twoorganizations jointly produced the H.262/MPEG-2 Video and H.264/MPEG-4Advanced Video Coding (AVC) and H.265/HEVC standards. Since H.262, thevideo coding standards are based on the hybrid video coding structurewherein temporal prediction plus transform coding are utilized. Toexplore the future video coding technologies beyond HEVC, Joint VideoExploration Team (WET) was founded by VCEG and MPEG jointly in 2015.Since then, many new methods have been adopted by JVET and put into thereference software named Joint Exploration Model (JEM). In April 2018,the Joint Video Expert Team (JVET) between VCEG (Q6/16) and ISO/IEC JTC1SC29/WG11 (MPEG) was created to work on the VVC standard targeting at50% bitrate reduction compared to HEVC.

The latest version of VVC draft, i.e., Versatile Video Coding (Draft 3)can be found athttp://phenix.it-sudparis.eu/jvet/doc_end_user/documents/12_Macao/wg11/JVET-L1001-v2.zip.The latest reference software of VVC, named VTM, can be found at:https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/tagsNTM-3.0rc1

2.1 Inter Prediction in HEVC/H.265

Each inter-predicted PU has motion parameters for one or two referencepicture lists. Motion parameters include a motion vector and a referencepicture index. Usage of one of the two reference picture lists may alsobe signaled using inter_pred_idc. Motion vectors may be explicitly codedas deltas relative to predictors.

When a CU is coded with skip mode, one PU is associated with the CU, andthere are no significant residual coefficients, no coded motion vectordelta or reference picture index. A merge mode is specified whereby themotion parameters for the current PU are obtained from neighboring PUs,including spatial and temporal candidates. The merge mode can be appliedto any inter-predicted PU, not only for skip mode. The alternative tomerge mode is the explicit transmission of motion parameters, wheremotion vector (to be more precise, motion vector differences (MVD)compared to a motion vector predictor), corresponding reference pictureindex for each reference picture list and reference picture list usageare signaled explicitly per each PU. Such a mode is named Advancedmotion vector prediction (AMVP) in this disclosure.

When signaling indicates that one of the two reference picture lists isto be used, the PU is produced from one block of samples. This istypically referred to as ‘uni-prediction’. Uni-prediction is availableboth for P-slices and B-slices.

When signaling indicates that both of the reference picture lists are tobe used, the PU is produced from two blocks of samples. This is referredto as ‘bi-prediction’. Bi-prediction is available for B-slices only.

The following text provides the details on the inter prediction modesspecified in HEVC. The description will start with the merge mode.

2.1.1 Reference Picture List

In HEVC, the term inter prediction is used to denote prediction derivedfrom data elements (e.g., sample values or motion vectors) of referencepictures other than the current decoded picture. Like in H.264/AVC, apicture canbe predicted from multiple reference pictures. The referencepictures that are used for inter prediction are organized in one or morereference picture lists. The referenceindex identifies which of thereference pictures in the list can be used for creating the predictionsignal.

A single reference picture list, List 0, is used for a P slice and tworeference picture lists, List 0 and List 1 are used for B slices.Reference pictures included in List 0/1 can be from past and futurepictures in terms of capturing/display order.

2.1.2 Merge Mode 2.1.2.1 Derivation of Candidates for Merge Mode

When a PU is predicted using merge mode, an index pointing to an entryin the merge candidates list is parsed from the bitstream and used toretrieve the motion information. The construction of this list isspecified in the HEVC standard and can be summarized according to thefollowing sequence of steps:

-   -   Step 1: Initial candidates derivation        -   Step 1.1: Spatial candidates derivation        -   Step 1.2: Redundancy check for spatial candidates        -   Step 1.3: Temporal candidates derivation    -   Step 2: Additional candidates insertion        -   Step 2.1: Creation of bi-predictive candidates        -   Step 2.2: Insertion of zero motion candidates

These steps are also schematically depicted in FIG. 1. For spatial mergecandidate derivation, a maximum of four merge candidates are selectedamong candidates that are located in five different positions. Fortemporal merge candidate derivation, a maximum of one merge candidate isselected among two candidates. Since constant number of candidates foreach PU is assumed at decoder, additional candidates are generated whenthe number of candidates obtained from step 1 does not reach the maximumnumber of merge candidate (MaxNumMergeCand) which is signaled in sliceheader. Since the number of candidates is constant, index of best mergecandidate is encoded using truncated unary binarization (TU). If thesize of CU is equal to 8, all the PUs of the current CU share a singlemerge candidate list, which is identical to the merge candidate list ofthe 2N×2N prediction unit.

In the following, the operations associated with the aforementionedsteps are detailed.

2.1.2.2 Spatial Candidates Derivation

In the derivation of spatial merge candidates, a maximum of four mergecandidates are selected among candidates located in the positionsdepicted in FIG. 2. The order of derivation is A₁, B₁, B₀, A₀ and B₂.Position B₂ is considered only when any PU of position A₁, B₁, B₀, A₀ isnot available (e.g. because it belongs to another slice or tile) or isintra coded. After candidate at position A₁ is added, the addition ofthe remaining candidates is subject to a redundancy check which ensuresthat candidates with same motion information are excluded from the listso that coding efficiency is improved. To reduce computationalcomplexity, not all possible candidate pairs are considered in thementioned redundancy check. Instead only the pairs linked with an arrowin FIG. 3 are considered and a candidate is only added to the list ifthe corresponding candidate used for redundancy check has not the samemotion information. Another source of duplicate motion information isthe “second PU” associated with partitions different from 2N×2N. As anexample, FIGS. 4A-4B depict the second PU for the case of N×2N and 2N×N,respectively. When the current PU is partitioned as N×2N, candidate atposition A_(l) is not considered for list construction. In fact, byadding this candidate will lead to two prediction units having the samemotion information, which is redundant to just have one PU in a codingunit. Similarly, position B₁ is not considered when the current PU ispartitioned as 2N×N.

2.1.2.3 Temporal Candidates Derivation

In this step, only one candidate is added to the list. Particularly, inthe derivation of this temporal merge candidate, a scaled motion vectoris derived based on co-located PU belonging to the picture which has thesmallest POC difference with current picture within the given referencepicture list. The reference picture list to be used for derivation ofthe co-located PU is explicitly signaled in the slice header. The scaledmotion vector for temporal merge candidate is obtained as illustrated bythe dotted line in FIG. 5, which is scaled from the motion vector of theco-located PU using the POC distances, tb and td, where tb is defined tobe the POC difference between the reference picture of the currentpicture and the current picture and td is defined to be the POCdifference between the reference picture of the co-located picture andthe co-located picture. The reference picture index of temporal mergecandidate is set equal to zero. A practical realization of the scalingprocess is described in the HEVC specification. For a B-slice, twomotion vectors, one is for reference picture list 0 and the other is forreference picture list 1, are obtained and combined to make thebi-predictive merge candidate.

FIG. 5 is an illustration of motion vector scaling for temporal mergecandidate.

In the co-located PU (Y) belonging to the reference frame, the positionfor the temporal candidate is selected between candidates C₀ and C₁, asdepicted in FIG. 6. If PU at position C₀ is not available, is intracoded, or is outside of the current coding tree unit (CTU aka. LCU,largest coding unit) row, position C₁ is used. Otherwise, position C_(o)is used in the derivation of the temporal merge candidate.

FIG. 6 shows examples of candidate positions for temporal mergecandidate, C0 and C1.

2.1.2.4 Additional Candidates Insertion

Besides spatial and temporal merge candidates, there are two additionaltypes of merge candidates: combined bi-predictive merge candidate andzero merge candidate. Combined bi-predictive merge candidates aregenerated by utilizing spatial and temporal merge candidates. Combinedbi-predictive merge candidate is used for B-Slice only. The combinedbi-predictive candidates are generated by combining the first referencepicture list motion parameters of an initial candidate with the secondreference picture list motion parameters of another. If these two tuplesprovide different motion hypotheses, they will form a new bi-predictivecandidate. As an example, FIG. 7 depicts the case when two candidates inthe original list (on the left), which have mvL0 and refIdxL0 or mvL0and refIdxL1, are used to create a combined bi-predictive mergecandidate added to the final list (on the right). There are numerousrules regarding the combinations which are considered to generate theseadditional merge candidates.

Zero motion candidates are inserted to fill the remaining entries in themerge candidates list and therefore hit the MaxNumMergeCand capacity.These candidates have zero spatial displacement and a reference pictureindex which starts from zero and increases every time a new zero motioncandidate is added to the list.

More specifically, the following steps are performed in order till themerge list is full:

-   -   1. Set variable numRef to either number of reference picture        associated with list 0 for P slice, or the minimum number of        reference pictures in two lists for B slice;    -   2. Add non-repeated zero motion candidates:        -   For variable i being 0 . . . numRef-1, add a default motion            candidate with MV set to (0, 0) and reference picture index            set to i for list 0 (if P slice), or for both lists (if B            slice).    -   3. Add repeated zero motion candidates with MV set to (0, 0),        reference picture index of list 0 set to 0 (if P slice) and        reference picture indices of both lists set to 0 (if B slice).

Finally, no redundancy check is performed on these candidates.

2.1.3 AMVP

AMVP exploits spatio-temporal correlation of motion vector withneighbouring PUs, which is used for explicit transmission of motionparameters. For each reference picture list, a motion vector candidatelist is constructed by firstly checking availability of left, abovetemporally neighbouring PU positions, removing redundant candidates andadding zero vector to make the candidate list to be constant length.Then, the encoder can select the best predictor from the candidate listand transmit the corresponding index indicating the chosen candidate.Similarly with merge index signaling, the index of the best motionvector candidate is encoded using truncated unary. The maximum value tobe encoded in this case is 2 (see FIG. 8). In the following sections,details about derivation process of motion vector prediction candidateare provided.

2.1.3.1 Derivation of AMVP Candidates

FIG. 8 summarizes derivation process for motion vector predictioncandidate.

In motion vector prediction, two types of motion vector candidates areconsidered: spatial motion vector candidate and temporal motion vectorcandidate. For spatial motion vector candidate derivation, two motionvector candidates are eventually derived based on motion vectors of eachPU located in five different positions as depicted in FIG. 2.

For temporal motion vector candidate derivation, one motion vectorcandidate is selected from two candidates, which are derived based ontwo different co-located positions. After the first list ofspatio-temporal candidates is made, duplicated motion vector candidatesin the list are removed. If the number of potential candidates is largerthan two, motion vector candidates whose reference picture index withinthe associated reference picture list is larger than 1 are removed fromthe list. If the number of spatio-temporal motion vector candidates issmaller than two, additional zero motion vector candidates is added tothe list.

2.1.3.2 Spatial Motion Vector Candidates

In the derivation of spatial motion vector candidates, a maximum oftwocandidates are considered among five potential candidates, which arederived from PUs located in positions as depicted in FIG. 2, thosepositions being the same as those of motion merge. The order ofderivation for the left side of the current PU is defined as A₀, A₁, andscaled A₀, scaled A₁. The order of derivation for the above side of thecurrent PU is defined as B₀, B₁, B₂, scaled B₀, scaled B₁, scaled B₂.For each side there are therefore four cases that can be used as motionvector candidate, with two cases not required to use spatial scaling,and two cases where spatial scaling is used. The four different casesare summarized as follows.

-   -   No spatial scaling        -   (1) Same reference picture list, and same reference picture            index (same POC)        -   (2) Different reference picture list, but same reference            picture (same POC)    -   Spatial scaling        -   (3) Same reference picture list, but different reference            picture (different POC)        -   (4) Different reference picture list, and different            reference picture (different POC)

The no-spatial-scaling cases are checked first followed by the spatialscaling Spatial scaling is considered when the POC is different betweenthe reference picture of the neighbouring PU and that of the current PUregardless of reference picture list. If all PUs of left candidates arenot available or are intra coded, scaling for the above motion vector isallowed to help parallel derivation of left and above MV candidates.Otherwise, spatial scaling is not allowed for the above motion vector.

In a spatial scaling process, the motion vector of the neighboring PU isscaled in a similar manner as for temporal scaling, as depicted in FIG.9. The main difference is that the reference picture list and index ofcurrent PU is given as input; the actual scaling process is the same asthat of temporal scaling.

2.1.3.3 Temporal Motion Vector Candidates

Apart for the reference picture index derivation, all processes for thederivation of temporal merge candidates are the same as for thederivation of spatial motion vector candidates (see FIG. 6). Thereference picture index is signaled to the decoder.

2.2 Sub-CU Based Motion Vector Prediction Methods in JEM

In the JEM with QTBT, each CU can have at most one set of motionparameters for each prediction direction. Two sub-CU level motion vectorprediction methods are considered in the encoder by splitting a large CUinto sub-CUs and deriving motion information for all the sub-CUs of thelarge CU. Alternative temporal motion vector prediction (ATMVP) methodallows each CU to fetch multiple sets of motion information frommultiple blocks smaller than the current CU in the collocated referencepicture. In spatial-temporal motion vector prediction (STMVP) methodmotion vectors of the sub-CUs are derived recursively by using thetemporal motion vector predictor and spatial neighboring motion vector.

To preserve more accurate motion field for sub-CU motion prediction, themotion compression for the reference frames is currently disabled.

FIG. 10 shows an example of ATMVP motion prediction for a CU.

2.2.1 Alternative Temporal Motion Vector Prediction

In the alternative temporal motion vector prediction (ATMVP) method, themotion vectors temporal motion vector prediction (TMVP) is modified byfetching multiple sets of motion information (including motion vectorsand reference indices) from blocks smaller than the current CU. Thesub-CUs are square N×N blocks (N is set to 4 by default).

ATMVP predicts the motion vectors of the sub -CUs within a CU in twosteps. The first step is to identify the corresponding block in areference picture with a so-called temporal vector. The referencepicture is called the motion source picture. The second step is to splitthe current CU into sub-CUs and obtain the motion vectors as well as thereference indices of each sub-CU from the block corresponding to eachsub-CU.

In the first step, a reference picture and the corresponding block isdetermined by the motion information of the spatial neighboring blocksof the current CU. To avoid the repetitive scanning process ofneighboring blocks, the first merge candidate in the merge candidatelist of the current CU is used. The first available motion vector aswell as its associated reference index are set to be the temporal vectorand the index to the motion source picture. This way, in ATMVP, thecorresponding block may be more accurately identified, compared withTMVP, wherein the corresponding block (sometimes called collocatedblock) is always in a bottom-right or center position relative to thecurrent CU.

In the second step, a corresponding block of the sub-CU is identified bythe temporal vector in the motion source picture, by adding to thecoordinate of the current CU the temporal vector. For each sub-CU, themotion information of its corresponding block (the smallest motion gridthat covers the center sample) is used to derive the motion informationfor the sub-CU. After the motion information of a corresponding N×Nblock is identified, it is converted to the motion vectors and referenceindices of the current sub-CU, in the same way as TMVP of HEVC, whereinmotion scaling and other procedures apply. For example, the decoderchecks whether the low-delay condition (i.e. the POCs of all referencepictures of the current picture are smaller than the POC of the currentpicture) is fulfilled and possibly uses motion vector MV_(x) ((themotion vector corresponding to reference picture list X) to predictmotion vector MV_(y) (with X being equal to 0 or 1 and Y being equal to1−X) for each sub-CU.

2.2.2 Spatial-Temporal Motion Vector Prediction (STMVP)

In this method, the motion vectors of the sub-CUs are derivedrecursively, following raster scan order. FIG. 11 illustrates thisconcept. For example, FIG. 11 shows a 8×8 CU with four 4×4 sub-CUs A, B,C, and D. The neighbouring 4×4 blocks in the current frame are labelledas a, b, c, and d.

The motion derivation for sub-CU A starts by identifying its two spatialneighbours. The first neighbour is the N×N block above sub-CU A (blockc). If this block c is not available or is intra coded the other N×Nblocks above sub-CU A are checked (from left to right, starting at blockc). The second neighbour is a block to the left of the sub-CU A (blockb). If block b is not available or is intra coded other blocks to theleft of sub-CU A are checked (from top to bottom, staring at block b).The motion information obtained from the neighbouring blocks for eachlist is scaled to the first reference frame for a given list. Next,temporal motion vector predictor (TMVP) of sub-block A is derived byfollowing the same procedure of TMVP derivation as specified in HEVC.The motion information of the collocated block at location D is fetchedand scaled accordingly. Finally, after retrieving and scaling the motioninformation, all available motion vectors (up to 3) are averagedseparately for each reference list. The averaged motion vector isassigned as the motion vector of the current sub-CU.

2.2.3 Sub-CU Motion Prediction Mode Signalling

The sub-CU modes are enabled as additional merge candidates and there isno additional syntax element required to signal the modes. Twoadditional merge candidates are added to merge candidates list of eachCU to represent the ATMVP mode and STMVP mode. Up to seven mergecandidates are used, if the sequence parameter set indicates that ATMVPand STMVP are enabled. The encoding logic of the additional mergecandidates is the same as for the merge candidates in the HM, whichmeans, for each CU in P or B slice, two more RD checks is needed for thetwo additional merge candidates.

In the JEM, all bins of merge index is context coded by CABAC. While inHEVC, only the first bin is context coded and the remaining bins arecontext by-pass coded.

2.3 Inter Prediction Methods in VVC

There are several new coding tools for inter prediction improvement,such as Adaptive motion vector difference resolution (AMVR) forsignaling MVD, affine prediction mode, Triangular prediction mode (TPM),ATMVP, Generalized Bi-Prediction (GBI), Bi-directional Optical flow(BIO).

2.3.1 Adaptive Motion Vector Difference Resolution

In HEVC, motion vector differences (MVDs) (between the motion vector andpredicted motion vector of a PU) are signalled in units of quarter lumasamples when use_integer_mv_flag is equal to 0 in the slice header. Inthe VVC, a locally adaptive motion vector resolution (LAMVR) isintroduced. In the VVC, MVD can be coded in units of quarter lumasamples, integer luma samples or four luma samples (i.e., ¼-pel, 1-pel,4-pel). The MVD resolution is controlled atthe codingunit (CU) level,and MVD resolution flags are conditionally signalled for each CU thathas at least one non-zero MVD components.

For a CU that has at least one non-zero MVD components, a first flag issignalled to indicate whether quarter luma sample MV precision is usedin the CU. When the first flag (equal to 1) indicates that quarter lumasample MV precision is not used, another flag is signalled to indicatewhether integer luma sample MV precision or four luma sample MVprecision is used.

When the first MVD resolution flag of a CU is zero, or not coded for aCU (meaning all MVDs in the CU are zero), the quarter luma sample MVresolution is used for the CU. When a CU uses integer-luma sample MVprecision or four-luma-sample MV precision, the MVPs in the AMVPcandidate list for the CU are rounded to the corresponding precision.

In the encoder, CU-level RD checks are used to determine which MVDresolution is to be used for a CU. That is, the CU-level RD check isperformed three times for each MVD resolution. To accelerate encoderspeed, the following encoding schemes are applied in the JEM.

-   -   During RD check of a CU with normal quarter luma sample MVD        resolution, the motion information of the current CU (integer        luma sample accuracy) is stored. The stored motion information        (after rounding) is used as the starting point for further small        range motion vector refinement during the RD check for the same        CU with integer luma sample and 4 luma sample MVD resolution so        that the time-consuming motion estimation process is not        duplicated three times.    -   RD check of a CU with 4 luma sample MVD resolution is        conditionally invoked. For a CU, when RD cost integer luma        sample MVD resolution is much larger than that of quarter luma        sample MVD resolution, the RD check of 4 luma sample MVD        resolution for the CU is skipped.

The encoding process is shown in FIG. 12. First, ¼ pel MV is tested andthe RD cost is calculated and denoted as RDCost0, then integer MV istested and the RD cost is denoted as RDCost1. If RDCost1<th*RDCost0(wherein th is a positive value), then 4-pel MV is tested; otherwise,4-pel MV is skipped. Basically, motion information and RD cost etc. arealready known for 1/4 p el MV when checking integer or 4-pel MV, whichcan be reused to speed up the encoding process of integer or 4-pel MV.

2.3.2 Triangular Prediction Mode

The concept of the triangular prediction mode (TPM) is to introduce anew triangular partition for motion compensated prediction. As shown inFIGS. 13A-13B, it splits a CU into two triangular prediction units, ineither diagonal or inverse diagonal direction. Each triangularprediction unit in the CU is inter-predicted using its ownuni-prediction motion vector and reference frame index which are derivedfrom a single uni-prediction candidate list. An adaptive weightingprocess is performed to the diagonal edge after predicting thetriangular prediction units. Then, the transform and quantizationprocess are applied to the whole CU. This mode is only applied to mergemode, (skip mode is treated as a special merge mode).

FIG. 13A-13B are illustrations of splitting a CU into two triangularprediction units (two splitting patterns). For example, FIG. 13A showsan example of a 135 degree partition type (splitting from top-leftcorner to bottom-right corner) and FIG. 13B shows an example of a 45degree splitting pattern.

2.3.2.1 Uni-Prediction Candidate List for TPM

The uni-prediction candidate list, named TPM motion candidate list,consists of five uni-prediction motion vector candidates. It is derivedfrom seven neighboring blocks including five spatial neighboring blocks(1 to 5) and two temporal co-located blocks (6 to 7), as shown in FIG.14. The motion vectors of the seven neighboring blocks are collected andput into the uni-prediction candidate list according in the order ofuni-prediction motion vectors, L0 motion vector of bi-prediction motionvectors, L1 motion vector of bi-prediction motion vectors, and averagedmotion vector of the L0 and L1 motion vectors of bi-prediction motionvectors. If the number of candidates is less than five, zero motionvector is added to the list. Motion candidates added in this list forTPM are called TPM candidates, motion information derived fromspatial/temporal blocks are called regular motion candidates.

More specifically, the following steps are involved:

-   -   1) Obtain regular motion candidates from A₁, B₁, B₀, A₀, B₂, Col        and Col2 (corresponding to block 1-7 in FIG. 14) with full        pruning operations when adding a regular motion candidate from        spatial neighboring blocks.    -   2) Set variable numCurrMergeCand=0    -   3) For each regular motion candidates derived from A₁, B₁, B₀,        A₀, B₂, Col and Col2, if not pruned and numCurrMergeCand is less        than 5, if the regular motion candidate is uni-prediction        (either from List 0 or List 1), it is directly added to the        merge list as an TPM candidate with numCurrMergeCand increased        by 1. Such a TPM candidate is named ‘originally uni-predicted        candidate’.        -   Full pruning is applied.    -   4) For each motion candidates derived from A₁, B₁, B₀, A₀, B₂,        Col and Col2, if not pruned, and numCurrMergeCand is less than        5, if the regular motion candidate is bi-prediction, the motion        information from List 0 is added to the TPM merge list (that is,        modified to be uni-prediction from List 0) as a new TPM        candidate and numCurrMergeCand increased by 1. Such a TPM        candidate is named ‘Truncated List0-predicted candidate’.        -   Full pruning is applied.    -   5) For each motion candidates derived from A₁, B₁, B₀, A₀, B₂,        Col and Col2, if not pruned, and numCurrMergeCand is less than        5, if the regular motion candidate is bi-prediction, the motion        information from List 1 is added to the TPM merge list (that is,        modified to be uni-prediction from List 1) and numCurrMergeCand        increased by 1. Such a TPM candidate is named ‘Truncated        Listl-predicted candidate’.        Full pruning is applied.    -   6) For each motion candidates derived from A₁, B₁, B₀, A₀, B₂,        Col and Col2, if not pruned, and numCurrMergeCand is less than        5, if the regular motion candidate is bi-prediction,    -   If List 0 reference picture's slice QP is smaller than List 1        reference picture's slice QP, the motion information of List 1        is firstly scaled to List 0 reference picture, and the average        of the two MVs (one is from original List 0, and the other is        the scaled MV from List 1) is added to the TPM merge list, such        a candidate is called averaged uni-prediction from List 0 motion        candidate and numCurrMergeCand increased by 1.    -   Otherwise, the motion information of List 0 is firstly scaled to        List 1 reference picture, and the average of the two MVs (one is        from original List 1, and the other is the scaled MV from        List 0) is added to the TPM merge list, such a TPM candidate is        called averaged uni-prediction from List 1 motion candidate and        numCurrMergeCand increased by 1.        Full pruning is applied.    -   7) If numCurrMergeCand is less than 5, zero motion vector        candidates are added.

When inserting a candidate to the list, if it has to be compared to allpreviously added candidates to see whether it is identical to one ofthem, such a process is called full pruning

2.3.2.2 Adaptive Weighting Process

After predicting each triangular prediction unit, an adaptive weightingprocess is applied to the diagonal edge between the two triangularprediction units to derive the final prediction for the whole CU. Twoweighting factor groups are defined as follows:

-   -   1^(st) weighting factor group: {7/8, 6/8, 4/8, 2/8, 1/8} and        {7/8, 4/8, 1/8} are used for the luminance and the chrominance        samples, respectively;    -   2^(nd) weighting factor group: {7/8, 6/8, 5/8, 4/8, 3/8, 2/8,        1/8} and {6/8, 4/8, 2/8} are used for the luminance and the        chrominance samples, respectively.

Weighting factor group is selected based on the comparison of the motionvectors of two triangular prediction units. The 2^(nd) weighting factorgroup is used when the reference pictures of the two triangularprediction units are different from each other or their motion vectordifference is larger than 16 pixels. Otherwise, the Pt weighting factorgroup is used.

2.3.2.3 Signaling of Triangular Prediction Mode (TPM)

One bit flag to indicate whether TPM is used may be firstly signaled.Afterwards, the indications of two splitting patterns (as depicted inFIGS. 13A-13B), and selected merge indices for each of the twopartitions are further signaled.

2.3.2.3.1 Signaling of TPM Flag

If the width and height of a luma block is denoted by W and H,respectively, the, for W*H<64, triangular prediction mode is disabled.

When one block is coded with affine mode, triangular prediction mode isalso disabled.

When one block is coded with merge mode, one bit flag may be signaled toindicate whether the triangular prediction mode is enabled or disabledfor the block.

The flag is coded with 3 contexts, based on the following equation:

Ctx index=((left block L available && L is coded with TPM?)1:0)+((Aboveblock A available && A is coded with TPM?)1:0);

FIG. 15 shows examples ofneighboringblocks (A and L) used for contextselection in TPM flag coding.

2.3.2.3.2 Signaling of an Indication of Two Splitting Patterns (asdepicted in FIG. 13), and Selected Merge Indices for Each of the TwoPartitions

It is noted that splitting patterns, merge indices of two partitions arejointly coded. Further, the merge indices are restricted so that the twopartitions cannot use the same reference index. Therefore, there are 2(splitting patterns)*N (maximum number of merge candidates)*(N−1)possibilities wherein N is set to 5. One indication is coded and themapping between the splitting patterns, two merge indices and codedindication are derived from the array defined below:

-   -   const uint8_t_g        TriangleCombination[TRIANGLE_MAX_NUM_CANDS][3]={0, 1, 0}, {1, 0,        1}, {1, 0, 2}, {0, 0, 1}, {0, 2, 0}, {1, 0, 3}, {1, 0, 4}, {1,        1, 0}, {0, 3, 0}, {0, 4, 0}, {0, 0, 2}, {0, 1, 2}, {1, 1, 2},        {0, 0, 4}, {0, 0, 3}, {0, 1, 3}, {0, 1, 4}, {1, 1, 4}, {1, 1,        3}, {1, 2, 1}, {1, 2, 0}, {0, 2, 1}, {0, 4, 3}, {1, 3, 0}, {1,        3, 2}, {1, 3, 4}, {1, 4, 0}, {1, 3, 1}, {1, 2, 3}, {1, 4, 1},        {0, 4, 1}, {0, 2, 3}, {1, 4, 2}, {0, 3, 2}, {1, 4, 3}, {0, 3,        1}, {0, 2, 4}, {1, 2, 4}, {0, 4, 2}, {0, 3, 4}};

-   splitting patterns (45 degree or 135    degree)=g_TriangleCombination[signaledindication][0];

-   Merge index of candidate A=g_TriangleCombination[signaled    indication][1];

-   Merge index of candidate B=g_TriangleCombination[signaled    indication][2];

Once the two motion candidates A and B are derived, the two partitions'(PU1 and PU2) motion information can be set either from A or B. WhetherPU1 uses the motion information of merge candidate A or B is dependenton the prediction directions of the two motion candidates. Table 1 showsthe relationship between two derived motion candidates A and B, with thetwo partitions.

TABLE 1 Derivation of partitions' motion information from derived twomerge candidates (A, B) Prediction Prediction PU1's motion PU2's motiondirection of A direction of B information information L0 L0 A (L0) B(L0) L1 L1 B (L1) A (L1) L0 L1 A (L0) B (L1) L1 L0 B (L0) A (L1)

2.3.2.3.3 Entropy Coding of the Indication (Denoted byMerge_Triangle_idx)

-   merge triangle idx is within the range [0, 39], inclusively. K-th    order Exponential Golomb (EG) code is used for binarization of merge    triangle idx wherein K is set to 1.

K-th Order EG

To encode larger numbers in fewer b its (at the expense ofu sing morebits to encode smaller numbers), this can be generalized using anonnegative integer parameter k. To encode a nonnegative integer x in anorder-k exp-Golomb code.

-   -   1. Encode └x/2^(x)┘ using order-0 exp-Golomb code described        above, then    -   2. Encode x mod 2^(k) in binary

TABLE 2 Exp-Golomb-k coding examples x k = 0 k = 1 k = 2 0 1 10 100 1010 11 101 2 011 0100 110 3 00100 0101 111 4 00101 0110 01000 5 001100111 01001 6 00111 001000 01010 7 0001000 001001 01011 8 0001001 00101001100 9 0001010 001011 01101 10 0001011 001100 01110 11 0001100 00110101111 12 0001101 001110 0010000 13 0001110 001111 0010001 14 000111100010000 0010010 15 000010000 00010001 0010011 16 000010001 000100100010100 17 000010010 00010011 0010101 18 000010011 00010100 0010110 19000010100 00010101 0010111

2.3.3 Affine Motion Compensation Prediction

In HEVC, only translation motion model is applied for motioncompensation prediction (MCP). While in the real world, there are manykinds of motion, e.g. zoom in/out, rotation, perspective motions and theother irregular motions. In VVC, a simplified affine transform motioncompensation prediction is applied with 4-parameter affine model and6-parameter affine model. As shown FIGS. 16A-16B, the affine motionfield of the block is described by two control point motion vectors(CPMVs) for the 4-parameter affine model (FIG. 16A) and 3 CPMVs for the6-parameter affine model (FIG. 16B).

The motion vector field (MVF) of a block is described by the followingequations with the 4-parameter affine model (wherein the 4-parameter aredefined as the variables a, b, e and f) in equation (1) and 6-parameteraffine model (wherein the 4-parameter are defined as the variables a, b,c, d, e and f) in equation (2) respectively:

$\begin{matrix}\left\{ \begin{matrix}{{m{v^{h}\left( {x,y} \right)}} = {{{ax} - {by} + e} = {{\frac{\left( {{mv_{1}^{h}} - {mv_{0}^{h}}} \right)}{w}x} - {\frac{\left( {{mv_{1}^{v}} - {mv_{0}^{v}}} \right)}{w}y} + {mv_{0}^{h}}}}} \\{{m{v^{v}\left( {x,y} \right)}} = {{{bx} + {ay} + f} = {{\frac{\left( {{mv_{1}^{v}} - {mv_{0}^{v}}} \right)}{w}x} + {\frac{\left( {{mv_{1}^{h}} - {mv_{0}^{h}}} \right)}{w}y} + {mv_{0}^{v}}}}}\end{matrix} \right. & (1) \\\left\{ \begin{matrix}{{m{v^{h}\left( {x,y} \right)}} = {{{ax} + {cy} + e} = {{\frac{\left( {{mv_{1}^{h}} - {mv_{0}^{h}}} \right)}{w}x} + {\frac{\left( {{mv_{2}^{h}} - {mv_{0}^{h}}} \right)}{h}y} + {mv_{0}^{h}}}}} \\{{m{v^{v}\left( {x,y} \right)}} = {{{bx} + {dy} + f} = {{\frac{\left( {{mv_{1}^{v}} - {mv_{0}^{v}}} \right)}{w}x} + {\frac{\left( {{mv_{2}^{v}} - {mv_{0}^{v}}} \right)}{h}y} + {mv_{0}^{v}}}}}\end{matrix} \right. & (2)\end{matrix}$

where (m^(vh) ₀, m^(vh) ₀) is motion vector of the top-left cornercontrol point, and (m^(vh) ₁, m^(vh) ₁) is motion vector of thetop-right corner control point and (m^(vh) ₂, m^(vh) ₂) is motion vectorof the bottom-left corner control point, all of the three motion vectorsare called control point motion vectors (CPMV), (x, y) represents thecoordinate of a representative point relative to the top-left samplewithin current block and (mv^(h)(x,y), mv^(v)(x,y)) is the motion vectorderived for a sample located at (x, y). The CP motion vectors may besignaled (like in the affine AMVP mode) or derived on-the-fly (like inthe affine merge mode). w and h are the width and height of the currentblock. In practice, the division is implemented by right-shift with arounding operation. In VTM, the representative point is defined to bethe center position of a sub-block, e.g., when the coordinate of theleft-top corner of a sub-block relative to the top-left sample withincurrent block is (xs, ys), the coordinate of the representative point isdefined to be (xs+2, ys+2). For each sub-block (i.e., 4×4 in VTM), therepresentative point is utilized to derive the motion vector for thewhole sub-block.

In order to further simplify the motion compensation prediction,sub-block based affine transform prediction is applied. To derive motionvector of each M×N (both M and N are set to 4 in current VVC) sub-block,the motion vector of the center sample of each sub-block, as shown inFIG. 17, is calculated according to Equation (1) and (2), and rounded to1/16 fraction accuracy. Then the motion compensation interpolationfilters for 1/16-pel are applied to generate the prediction of eachsub-block with derived motion vector. The interpolation filters for1/16-pel are introduced by the affine mode.

After MCP, the high accuracy motion vector of each sub-block is roundedand saved as the same accuracy as the normal motion vector.

2.3.3.1 Signaling of Affine Prediction

Similar to the translational motion model, there are also two modes forsignaling the side information due affine prediction. They areAFFINE_INTER and AFFINE_MERGE modes.

2.3.3.2 AF_INTER Mode

For CUs with both width and height larger than 8, AF_INTER mode can beapplied. An affine flag in CU level is signalled in the bitstream toindicate whether AF_INTER mode is used.

In this mode, for each reference picture list (List 0 or List 1), anaffine AMVP candidate list is constructed with three types of affinemotion predictors in the following order, wherein each candidateincludes the estimated CPMVs of the current block. The differences ofthe best CPMVs found at the encoder side (such as mv₀ mv₁ mv₂ in FIG.20) and the estimated CPMVs are signalled. In addition, the index ofaffine AMVP candidate from which the estimated CPMVs are derived isfurther signalled.

1) Inherited Affine Motion Predictors

The checking order is similar to that of spatial MVPs in HEVC AMVP listconstruction. First, a left inherited affine motion predictor is derivedfrom the first block in {A1, A0} that is affine coded and has the samereference picture as in currentblock. Second, an above inherited affinemotion predictor is derived from the first block in {B1, B0, B2} that isaffine coded and has the same reference picture as in current block. Thefive blocks A1, A0, B1, B0, B2 are depicted in FIG. 19.

Once a neighboring block is found to be coded with affine mode, theCPMVs of the codingunit covering the neighboringblock are used to derivepredictors of CPMVs of current block. For example, if A1 is coded withnon-affine mode and A0 is coded with 4-parameter affine mode, the leftinherited affine MV predictor will be derived from A0. In this case, theCPMVs of a CU covering A0, as denoted by MV₀ ^(N) for the top-left CPMVand MV₁ ^(N) for the top-right CPMV in FIG. 21B are utilized to derivethe estimated CPMVs of current block, denoted by MV₀ ^(V), MV₁ ^(C), MV₂^(C) for the top-left (with coordinate (x0, y0)), top-right (withcoordinate (x1, y1)) and bottom-right positions (with coordinate (x2,y2)) of current block.

2) Constructed Affine Motion Predictors

A constructed affine motion predictor consists of control-point motionvectors (CPMVs) that are derived from neighboring inter coded blocks, asshown in FIG. 20, that have the same reference picture. If the currentaffine motion model is 4-parameter affine, the number of CPMVs is 2,otherwise if the current affine motion model is 6-parameter affine, thenumber of CPMVs is 3. The top-left CPMV mv ₀ is derived by the MV at thefirst block in the group {A, B, C} that is inter coded and has the samereference picture as in current block. The top-right CPMV mv ₁ isderived by the MV at the first block in the group {D, E} that is intercoded and has the same reference picture as in current block. Thebottom-left CPMV mv ₂ is derived by the MV at the first block in thegroup {F, G} that is inter coded and has the same reference picture asin current block.

-   -   If the current affine motion model is 4-parameter affine, then a        constructed affine motion predictor is inserted into the        candidate list only if both mv ₀ and mv ₁ are founded, that is,        mv ₀ and mv ₁ are used as the estimated CPMVs for top-left (with        coordinate (x0, y0)), top-right (with coordinate (x1, y1))        positions of current block.    -   If the current affine motion model is 6-parameter affine, then a        constructed affine motion predictor is inserted into the        candidate list only if mv ₀, mv ₁ and mv ₂ are all founded, that        is, mv ₀, mv ₁ and mv ₂ are used as the estimated CPMVs for        top-left (with coordinate (x0, y0)), top-right (with coordinate        (x1, y1)) and bottom-right (with coordinate (x2, y2)) positions        of current block.

No pruning process is applied when inserting a constructed affine motionpredictor into the candidate list.

3) Normal AMVP Motion Predictors

The following applies until the number of affine motion predictorsreaches the maximum.

-   -   1) Derive an affine motion predictor by setting all CPMVs equal        to mv ₂ if available.    -   2) Derive an affine motion predictor by setting all CPMVs equal        to mv ₁ if available.    -   3) Derive an affine motion predictor by setting all CPMVs equal        to mv ₎ if available.    -   4) Derive an affine motion predictor by setting all CPMVs equal        to HEVC TMVP if available.    -   5) Derive an affine motion predictor by setting all CPMVs to        zero MV.

Note that mv ₁ is already derived in constructed affine motionpredictor.

FIG. 18A shows an example of a 4-parameter affine model. FIG. 18B showsan example of a 6-parameter affine model.

FIG. 19 shows an example of MVP for AF_INTER for inherited affinecandidates.

FIG. 20 shows an example of MVP for AF_INTER for constructed affinecandidates.

In AF_INTER mode, when 4/6-parameter affine mode is used, 2/3 controlpoints are required, and therefore 2/3 MVD needs to be coded for thesecontrol points, as shown in FIG. 18. In JVET-K0337, it is proposed toderive the MV as follows, i.e., mvd₁ and mvd₂ are predicted from mvd₀.

mv ₀ =mv ₀ +mvd ₀

mv ₁ =mv ₁ +mvd ₁ +mvd ₀

mv ₂ =mv ₂ +mvd ₂ +mvd ₀

Wherein mv ₁, mvd_(i) and mv₁ are the predicted motion vector, motionvector difference and motion vector of the top-left pixel (i=0),top-right pixel (i=1) or left-bottom pixel (i=2) respectively, as shownin FIG. 18B. Please note that the addition of two motion vectors (e.g.,mvA(xA, yA) and mvB(xB, yB)) is equal to summation of two componentsseparately, that is, newMV=mvA+mvB and the two components of newMV isset to (xA+xB) and (yA+yB), respectively.

2.3.3.3 AF_MERGE Mode

When a CU is applied in AF_MERGE mode, it gets the first block codedwith affine mode from the valid neighbor reconstructed blocks. And theselection order for the candidate block is from left, above, aboveright, left bottom to above left as shown in FIG. 21A (denoted by A, B,C, D, E in order). For example, if the neighbor left bottom block iscoded in affine mode as denoted by A0 in FIG. 21B, the Control Point(CP) motion vectors mv₀ ^(N), mv₁ ^(N) and mv₂ ^(N) of the top leftcorner, above right corner and left bottom corner of the neighboringCU/PU which includes the block A are fetched. And the motion vector mv₀^(C), mv₁ ^(C) and mv₂ ^(C) (which is only used for the 6-parameteraffine model) of the top left corner/top right/bottom left on thecurrent CU/PU is calculated based on mv₀ ^(N), mv₁ ^(N) and mv₂ ^(N). InVTM-2.0, sub-block (e.g 4 ×4 block in VTM) located at the top-leftcorner stores mv0, the sub-block located at the top-right corner storesmy 1 if the current block is affine coded. If the current block is codedwith the 6-parameter affine model, the sub-block located at thebottom-left corner stores mv2; otherwise (with the 4-parameter affinemodel), LB stores mv2′. Other sub-blocks stores the MVs used for MC.

After the CPMV of the current CU mv₀ ^(C), mv₁ ^(C) and mv₂ ^(C) arederived, according to the simplified affine motion model Equation (1)and (2), the MVF of the current CU is generated. In order to identifywhether the current CU is coded with AF_MERGE mode, an affine flag issignaled in the bitstream when there is at least one neighbor block iscoded in affine mode.

In JVET-L0142 and JVET-L0632, an affine merge candidate list isconstructed with following steps:

1) Insert Inherited Affine Candidates

Inherited affine candidate means that the candidate is derived from theaffine motion model of its valid neighbor affine coded block. Themaximum two inherited affine candidates are derived from affine motionmodel of the neighboring blocks and inserted into the candidate list.For the left predictor, the scan order is {A0, A1}; for the abovepredictor, the scan order is {B0, B1, B2}.

2) Insert Constructed Affine Candidates

If the number of candidates in affine merge candidate list is less thanMaxNumAffineCand (e.g., 5), constructed affine candidates are insertedinto the candidate list Constructed affine candidate means the candidateis constructed by combining the neighbor motion information of eachcontrol point.

-   -   a) The motion information forthe control points is derived        firstly from the specified spatial neighbors and temporal        neighbor shown in FIG. 22. CPk (k=1, 2, 3, 4) represents the        k-th control point. A0, A1, A2, B0, B1, B2 and B3 are spatial        positions for predicting CPk (k=1, 2, 3); T is temporal position        for predicting CP4.

The coordinates of CP1, CP2, CP3 and CP4 is (0, 0), (W, 0), (H, 0) and(W, H), respectively, where W and H are the width and height of currentblock.

The motion information of each control point is obtained according tothe following priority order:

-   -   For CP1, the checking priority is B2->B3->A2. B2 is used if it        is available. Otherwise, if B2 is available, B3 is used. If both        B2 and B3 are unavailable, A2 is used. If all the three        candidates are unavailable, the motion information of CP1 cannot        be obtained.    -   For CP2, the checking priority is B1->B0.    -   For CP3, the checking priority is A1->A0.    -   For CP4, T is used.    -   b) Secondly, the combinations of controls points are used to        construct an affine merge candidate.        -   I. Motion information of three control points are needed to            construct a 6-parameter affine candidate. The three control            points can be selected from one of the following four            combinations ({CP1, CP2, CP4}, {CP1, CP2, CP3}, {CP2, CP3,            CP4}, {CP1, CP3, CP4}). Combinations {CP1, CP2, CP3}, {CP2,            CP3, CP4}, {CP1, CP3, CP4} will be converted to a            6-parameter motion model represented by top-left, top-right            and bottom-left control points.        -   II. Motion information of two control points are needed to            construct a 4-parameter affine candidate. The two control            points can be selected from one of the two combinations            ({CP1, CP2}, {CP1, CP3}). The two combinations will be            converted to a 4-parameter motion model represented by            top-left and top-right control points.        -   III. The combinations of constructed affine candidates are            inserted into to candidate list as following order:            -   {CP1, CP2, CP3}, {CP1, CP2, CP4}, {CP1, CP3, CP4}, {CP2,                CP3, CP4}, {CP1, CP2}, {CP1, CP3}            -   i. For each combination, the reference indices of list X                for each CP are checked, if they are all the same, then                this combination has valid CPMVs for list X. If the                combination does not have valid CPMVs for both list 0                and list 1, then this combination is marked as invalid.                Otherwise, it is valid, and the CPMVs are put into the                sub-block merge list.                3) Padding with Xero Motion Vectors

If the number of candidates in affine merge candidate list is less than5, zero motion vectors with zero reference indices are insert into thecandidate list, until the list is full.

More specifically, for the sub-block merge candidate list, a 4-parametermerge candidate with MVs set to (0, 0) and prediction direction set touni-prediction from list 0 (for P slice) and bi-prediction (for Bslice).

2.3.4 Current Picture Referencing

Intra block copy (a.k.a. IBC, or intra picture block compensation), alsonamed current picture referencing (CPR) was adopted in HEVC screencontent coding extensions (SCC). This tool is very efficient for codingof screen content video in that repeated patterns in text and graphicsrich content occur frequently within the same picture. Having apreviously reconstructed block with equal or similar pattern as apredictor can effectively reduce the prediction error and thereforeimprove coding efficiency. An example of the intra block compensation isillustrated in FIG. 23.

Similar to the design of CRP in HEVC SCC, In VVC, The use of the IBCmode is signaled at both sequence and picture level. When the IBC modeis enabled at sequence parameter set (SPS), it can be enabled at picturelevel. When the IBC mode is enabled at picture level, the currentreconstructed picture is treated as a reference picture. Therefore, nosyntax change on block level is needed on top of the existing VVC intermode to signal the use of the IBC mode.

Main features:

-   -   It is treated as a normal inter mode. Therefore, merge and skip        modes are also available for the IBC mode. The merge candidate        list construction is unified, including merge candidates from        the neighboring positions that are either coded in the IBC mode        or the HEVC inter mode. Depending on the selected merge index,        the current block under merge or skip mode can merge into either        an IBC mode coded neighbor or otherwise an normal inter mode        coded one with different pictures as reference pictures.    -   Block vector prediction and coding schemes for the IBC mode        reuse the schemes used for motion vector prediction and coding        in the HEVC inter mode (AMVP and MVD coding).    -   The motion vector for the IBC mode, also referred as block        vector, is codedwith integer-pel precision, but stored in memory        in 1/16-pel precision after decoding as quarter-pel precision is        used in interpolation and deblocking stages. When used in motion        vector prediction for the IBC mode, the stored vector predictor        will be right shifted by 4.    -   Search range: it is restricted to be within the current CTU.    -   CPR is disallowed when affine mode/triangular mode/GBI/weighted        prediction is enabled.

2.3.5 Merge List Design in VVC

There are three different merge list construction processes supported inVVC:

-   -   1) Sub-block merge candidate list: it includes ATMVP and affine        merge candidates. One merge list construction process is shared        for both affine modes and ATMVP mode. Here, the ATMVP and affine        merge candidates may be added in order. Sub-block merge list        size is signaled in slice header, and maximum value is 5.    -   2) Uni-Prediction TPM merge list: For triangular prediction        mode, one merge list construction process for the two partitions        is shared even two partitions can select their own merge        candidate index. When constructing this merge list, the spatial        neighbouring blocks and two temporal blocks of the block are        checked. The motion information derived from spatial neighbours        andtemporal blocks are called regular motion candidates in our        IDF. These regular motion candidates are further utilized to        derive multiple TPM candidates. Please note the transform is        performed in the whole block level, even two partitions may use        different motion vectors for generating their own prediction        blocks. Uni-Prediction TPM merge list size is fixed to be 5.    -   3) Regular merge list: For remaining coding blocks, one merge        list construction process is shared. Here, the        spatial/temporal/HMVP, pairwise combined bi-prediction merge        candidates and zero motion candidates may be inserted in order.        Regular merge list size is signaled in slice header, and maximum        value is 6.

2.3.5.1 Sub-Block Merge Candidate List

It is suggested that all the sub-block related motion candidates are putin a separate merge list in addition to the regular merge list fornon-sub block merge candidates.

The sub-block related motion candidates are put in a separate merge listis named as ‘sub-block merge candidate list’.

In one example, the sub-block merge candidate list includes affine mergecandidates, and ATMVP candidate, and/or sub-block based STMVP candidate.

2.3.5.1.1 JVET-L0278

In this contribution, the ATMVP merge candidate in the normal merge listis moved to the first position of the affine merge list. Such that allthe merge candidates in the new list (i.e., sub-block based mergecandidate list) are based on sub-block coding tools.

2.3.5.1.2 ATMVP in VTM-3.0

In VTM-3.0, a special merge candidate list, known as sub-block mergecandidate list (a. k. a affine merge candidate list) is added besidesthe regular merge candidate list. The sub-block merge candidate list isfilled with candidates in the following order:

-   -   a. ATMVP candidate (maybe available or unavailable);    -   b. Inherited Affine candidates;    -   c. Constructed Affine candidates;    -   d. Padding as zero MV 4-parameter affine model

The maximum number of candidates (denoted as ML) in the sub-block mergecandidate list derived as below:

-   -   1) If the ATMVP usage flag (e.g. the flag may be named as        “sps_sbtmvp_enabled_flag”) is on (equal to 1), but the affine        usage flag (e.g. the flag may be named as        “sps_affine_enabled_flag”) is off (equal to 0), then ML is set        equal to 1.    -   2) If the ATMVP usage flag is off (equal to 0), and the affine        usage flag is off (equal to 0), then ML is set equal to 0. In        this case, the sub-block merge candidate list is not used.    -   3) Otherwise (the affine usage flag is on (equal to 1), the        ATMVP usage flag is on or off), ML is signaled from the encoder        to the decoder. Valid ML is 0<=ML<=5.

When construct the sub-block merge candidate list, ATMVP candidate ischecked first. If any one of the following conditions is true, ATMVPcandidate is skipped and not put into the sub-block merge candidatelist.

-   -   1) The ATMVP usage flag is off;    -   2) Any TMVP usage flag (e.g. the flag may be named as        “slice_temporal_mvp_enabled_flag” when signaled at slice level)        is off;    -   3) The reference picture with reference index 0 in reference        list 0 is identical to the current picture (It is a CPR)

ATMVP in VTM-3.0 is much simpler than in JEM. When an ATMVP mergecandidate is generated, the following process is applied:

-   -   a. Check neighbouring blocks A1, B1, B0, A0 as shown in FIG. 22        in order, to find the first inter-coded, but not CPR-coded        block, denoted as block X;    -   b. Initialize TMV=(0,0). If there is a MV (denoted as MV′) of        block X, referring to the collocated reference picture (as        signaled in the slice header), TMV is set equal to MV′.    -   c. Suppose the center point of the current block is (x0, y0),        then locate a corresponding position of (x0,y0) as M=(x0+MV′x,        y0+MV′y) in the collocated picture. Find the block Z covering M.        -   i. If Z is intra-coded, then ATMVP is unavailable;        -   ii. If Z is inter-coded, MVZ_0 and MVZ_1 for the two lists            of block Z are scaled to (Reflist 0 index 0) and (Reflist 1            index 0) as MVdefault0, MVdefault1, and stored.    -   d. For each 8×8 sub-block, suppose its center point is (x0S,        yOS), then locate a corresponding position of (x0S, y0S) as        MS=(x0S+MV′x, y0S+MV′y) in the collocated picture. Find the        block ZS covering MS.        -   i. If ZS is intra-coded, MVdefault0, MVdefault1 are assigned            to the sub-block;        -   ii. If ZS is inter-coded, MVZS_0 and MVZS_1 for the two            lists of block ZS are scaled to (Reflist 0 index 0) and            (Reflist 1 index 0) and are assigned to the sub-block;

MV clipping and masking in ATMVP:

When locating a corresponding position such as M or MS in the collocatedpicture, it is clipped to be inside a predefined region. The CTU size isS×S, S=128 in VTM-3 .0. Suppose the top-left position of the collocatedCTU is (xCTU, yCTU), then the corresponding position M or MS at (xN, yN)will be clipped into the valid region xCTU<=xN<xCTU+S+4;yCTU<=yN<yCTU+S.

Besides Clipping, (xN, yN) is also masked as xN=xN&MASK, yN=yN&MASK,where MASK is an integer equal to ˜(2^(N)−1), and N=3, to set the lowest3 bits to be 0. So xN and yN are numbers which are times of 8. (“”represents the bitwise complement operator).

FIG. 24 shows an example of a valid corresponding region in thecollocated picture.

2.3.5.1.3 Syntax Design in Slice Header

 if( sps_temporal_mvp_enabled_flag )   slice_temporal_mvp_enabled_flagu(1)  if( slice_type == B )   mvd_l1_zero_flag u(1)  if(slice_temporal_mvp_enabled_flag ) {   if( slice_type == B )   collocated_from_l0_flag u(1)  } ...  if(!sps_affine_enabled_flag){   if(!sps_sbtmvp_enabled_flag)     MaxSubBlockMergeListSize = 0    else    MaxSubBlockMergeListSize = 1  }  else{   five_minus_max_num_affine_merge_cand ue(v)   MaxSubBlockMergeListSize = 5− five_minus_max_num_affine_merge_cand  }

2.3.5.2 Regular Merge List

Different from the merge list design, in VVC, the history-based motionvector prediction (HMVP) method is employed.

In HMVP, the previously coded motion information is stored. The motioninformation of a previously coded block is defined as an HMVP candidate.Multiple HMVP candidates are stored in a table, named as the HMVP table,and this table is maintained during the encoding/decoding processon-the-fly. The HMVP table is emptied when starting coding/decoding anew slice. Whenever there is an inter-coded block, the associated motioninformation is added to the last entry of the table as a new HMVPcandidate. The overall coding flow is depicted in FIG. 25.

HMVP candidates can be used in both AMVP and merge candidate listconstruction processes. FIG. 26 depicts the modified merge candidatelist construction process (shown with highlighted blocks in FIG. 26).When the merge candidate list is not full after the TMVP candidateinsertion, HMVP candidates stored in the HMVP table can be utilized tofill in the merge candidate list. Considering that one block usually hasa higher correlation with the nearest neighbouring block in terms ofmotion information, the HMVP candidates in the table are inserted in adescending order of indices. The last entry in the table is firstlyadded to the list, while the first entry is added in the end. Similarly,redundancy removal is applied on the HMVP candidates. Once the totalnumber of available merge candidates reaches the maximal number of mergecandidates allowed to be signaled, the merge candidate list constructionprocess is terminated.

2.4 MV Rounding

In VVC, when MV is right shifted, it is asked to be rounded toward zero.In a formulated way, for a MV(MVx, MVy) to be right shifted with N bits,the result MV′ (MVx′, MVy′) will be derived as:

MVx′=(MVx+((1<<N)>>1)−(MVx>=0? 1:0))>>N;

MVy′=(MVy+((1<<N)>>1)−(MVy>=0? 1:0))>>N;

2.5 RPR in JVET-O2001-v14

ARC, a.k.a. RPR (Reference Picture Resampling) is incorporated inWET-O2001-v14.

With RPR in JVET-O2001-v14, TMVP is disabled if the collocated picturehas a different resolution to the current picture. Besides, BDOF andDMVR are disabled when the reference picture has a different resolutionto the current picture.

To handle the normal MC when the reference picture has a differentresolutionthan the current picture, the interpolation section is definedas below:

8.5.6.3 Fractional Sample Interpolation Process 8.5.6.3.1 General

Inputs to this process are:

-   a luma location (xSb, ySb) specifying the top-left sample of the    current coding subblock relative to the top-left luma sample of the    current picture,-   a variable sbWidth specifying the width of the current coding    subblock,-   a variable sbHeight specifying the height of the current coding    subblock,-   a motion vector offset mvOffset,-   a refined motion vector refMvLX,-   the selected reference picture sample array refPicLX,-   the half sample interpolation filter index hpelIfIdx,-   the bi-directional optical flow flag bdofFlag,-   a variable cIdx specifying the colour component index of the current    block.

Outputs of this process are:

-   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array predSamplesLX of    prediction sample values.

The prediction block border extension size brdExtSize is derived asfollows:

brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb]&&sps_affine_prof_enabled_flag)) ? 2:0   (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of thereference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of thereference picture in luma samples.

The motion vector mvLX is set equal to (refMvLX−mvOffset).

-   If cIdx is equal to 0, the following applies:    -   The scaling factors and their fixed-point representations are        defined as

hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)

vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)

-   -   Let (xIntL, yIntL) be a luma location given in full-sample units        and (xFracL, yFracL) be an offset given in 1/16-sample units.        These variables are used only in this clause for specifying        fractional-sample locations inside the reference sample arrays        refPicLX.    -   The top-left coordinate of the bounding block for reference        sample padding (xSbInt_(L), ySbInt_(L)) is set equal to        (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).    -   For each luma sample location (x_(L)=0..sbWidth−1+brdExtSize,        y_(L)=0..sbHeight−1+brdExtSize) inside the prediction luma        sample array predSamplesLX, the corresponding prediction luma        sample value predSamplesLX[x_(L)][y_(L)] is derived as follows:        -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be            luma locations pointed to by a motion vector (refMvLX[0],            refMvLX[1]) given in 1/16-sample units. The variables            refxSb_(L), refx_(L), refySb_(L), and refy_(L) are derived            as follows:

refxSb _(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp   (8-755)

refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x_(L)*((hori_scale_fp+8)>>4))+32)>>6   (8-756)

refySb _(L)=((ySb<<4)+refMvLX[1])*vert_scale_fp   (8-757)

refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))+32)>>6   (8-758)

-   -   -   The variables xInt_(L), yInt_(L), xFrac_(L) and yFrac_(L)            are derived as follows:

xInt_(L)=refx_(L)>>4   (8-759)

yInt_(L)=refy_(L)>>4   (8-760)

xFrac_(L)=refx_(L)&15   (8-761)

yFrac_(L)=refy_(L)&15   (8-762)

-   -   If bdofFlag is equal to TRUE or (sps affine_prof enabled flag is        equal to TRUE and inter affine flag[xSb][ySb] is equal to TRUE),        and one or more of the following conditions are true, the        prediction luma sample value predSamplesLX[x_(L)][y_(L)] is        derived by invoking the luma integer sample fetching process as        specified in clause 8.5.6.3.3 with (xInt_(L)+(xFrac_(L)>>3)−1),        yInt_(L)+(yFrac_(L)>>3)−1) and refPicLX as inputs.        -   1. x_(L) is equal to 0.        -   2. x_(L) is equal to sbWidth+1.        -   3. yL is equal to 0.    -   4. y_(L) i s equal to sbHeight+1.    -   Otherwise, the prediction luma sample value        predSamplesLX[xL][yL] is derived by invoking the luma sample        8-tap interpolation filtering process as specified in clause        8.5.6.3.2 with (xIntL−(brdExtSize>0 ? 1:0), yIntL−(brdExtSize>0        ? 1:0)), (xFracL, yFracL), (xSbInt_(L), ySbInt_(L)), refPicLX,        hpelIfIdx, sbWidth, sbHeight and (xSb, ySb) as inputs.

-   Otherwise (cIdx is not equal to 0), the following applies:    -   Let (xIntC, yIntC) be a chroma location given in full-sample        units and (xFracC, yFracC) be an offset given in 1/32 sample        units. These variables are used only in this clause for        specifying general fractional-sample locations inside the        reference sample arrays refPicLX.    -   The top-left coordinate of the bounding block for reference        sample padding (xSbIntC, ySbIntC) is set equal to        ((xSb/SubWidthC)+(mvLX[0]>>5), (ySb/SubHeightC)+(mvLX[1]>>5)).    -   For each chroma sample location (xC=0..sbWidth−1, yC=0..        sbHeight 1) inside the prediction chroma sample arrays        predSamplesLX, the corresponding prediction chroma sample value        predSamplesLX[xC][yC ] is derived as follows:        -   Let (refx Sb_(C), refySb_(C)) and (refx_(C), refy_(C)) be            chroma locations pointed to by a motion vector (mvLX[0],            mvLX[1]) given in 1/32-sample units. The variables            refxSb_(C), refySb_(C), refx_(C) and refy_(C) are derived as            follows:

refxSb _(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp   (8-763)

refx _(C)=((Sign(refxSb _(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5   (8-764)

refySb _(C)=((ySb/SubHeightC<<5)+mvLX[1])*vert_scale_fp   (8-765)

refy _(C)=((Sign(refySb _(C))*(Abs(refySb _(C))+256)>>9)+yC*((vert_scalefp+8)>>4))+16)>>5   (8-766)

-   -   -   The variables xInt_(C), yInt_(C), xFrac_(C) and yFrac_(C)            are derived as follows:

xInt_(C)=refx _(C)>>5   (8-767)

yInt_(C)=refy _(C)>>5   (8-768)

xFrac_(C)=refy _(C)& 31   (8-769)

yFrac_(C)=refy _(C)& 31 (8-770)

-   -   The prediction sample value predSamplesLX[xC][yC] is derived by        invoking the process specified in clause 8.5.6.3.4 with (xIntC,        yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC), sbWidth, sbHeight        and refPicLX as inputs.

8.5.6.3.2 Luma Sample Interpolation Filtering Process

Inputs to this process are:

-   a luma location in full-sample units (xInt_(L), yInt_(L)),-   a luma location in fractional-sample units (xFrac_(L), yFrac_(L)),-   a luma location in full-sample units (xSbInt_(L), ySbInt_(L))    specifying the top-left sample of the bounding block for reference    sample padding relative to the top-left luma sample of the reference    picture,-   the luma reference sample array refPicLX_(L),-   the half sample interpolation filter index hpelIfIdx,-   a variable sbWidth specifying the width of the current subblock,-   a variable sbHeight specifying the height of the current subblock,-   a luma location (xSb, ySb) specifying the top-left sample of the    current subblock relative to the top-left luma sample of the current    picture,

Output of this process is a predicted luma sample value predSampleLX_(L)

The variables shiftl, shift2 and shift3 are derived as follows:

-   The variable shiftl is set equal to Min(4, BitDepth_(Y)−8), the    variable shift2 is set equal to 6 and the variable shift3 is set    equal to Max(2, 14−BitDepth_(Y)).-   The variable picW is set equal to pic_width_in_luma_samples and the    variable picH is set equal to pic_height_in_luma_samples.

The luma interpolation filter coefficients f_(L)[p] for each 1/16fractional sample position p equal to xFrac_(L) or yFrac_(L) are derivedas follows:

-   If MotionModelldc[xSb][ySb] is greater than 0, and sbWidth and    sbHeight are both equal to 4, the luma interpolation filter    coefficients f_(L)[p] are specified in Table 8-12.-   Otherwise, the luma interpolation filter coefficients f_(L)[p] are    specified in Table 8-11 depending on hpellfIdx.

The luma locations in full-sample units (xInt_(i), yInt_(i)) are derivedas follows for i=0..7:

-   If subpic treated as pic flag[SubPicIdx] is equal to 1, the    following applies:

xInt_(i)=Clip3(SubPicLeftBoundaryPos, SubPicRightBoundaryPos, xInt_(L)+i−3)   (8-771)

yInt_(i)=Clip3(SubPicTopBoundaryPos, SubPicBotBoundaryPos, yInt_(L)+i−3)   (8-772)

-   Otherwise (subpic treated as_pic flag[ SubPicIdx ] is equal to 0),    the following applies:

xInt_(i)=Clip3 (0, picW−1, sps_ref_wraparound_enabled_flag ?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY, picW, xInt_(L)+i−3 ):    (8-773)

xInt_(L) +i−3) yInt_(i)=Clip3(0, picH−1, yInt_(L) +i−3)   (8-774)

The luma locations in full-sample units are further modified as followsfor i=0..7:

xInt_(i)=Clip3(xSbInt_(L)−3, xSbInt_(L) +sbWidth+4, xInt_(i))   (8-775)

yInt_(i)=Clip3(ySbInt_(L)−3, ySbInt_(L) +sbHeight+4, yInt_(i))   (8-776)

The predicted luma sample value predSampleLX_(L) is derived as follows:

-   If both xFrac_(L) and yFrac_(L) are equal to 0, the value of    predSampleLX_(L) is derived as follows:

predSampleLX _(L)=refPicLX _(L) [xInt₃ ][yInt₃]<<shift3   (8-777)

-   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is equal to    0, the value of predSampleLX_(L) is derived as follows:

predSampleLX_(L)=(Σ_(i=0) ⁷ f _(L) [xFrac_(L) ][i]*refPicLX _(L)[xInt_(i) ][yInt₃])>>shift1   (8-778)

-   Otherwise, if xFrac_(L) is equal to 0 and yFrac_(L) is not equal to    0, the value of predSampleLX_(L) is derived as follows:

predSampleLX _(L)=(Σ_(i=0) ⁷ [f _(L) ][yFrac_(L) ][i]*refPicLX _(L)[xInt₃][yInt_(i)])>>shift1   (8-779)

-   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is not equal    to 0, the value of predSampleLX_(L) is derived as follows:    -   The sample array temp[n ] with n=0..7, is derived as follows:

temp[n]=(Σ_(i=0) ⁷ f _(L) [xFrac_(L) ][i]*refPicLX _(L) [xInt_(i)][yInt_(n)])>>shift1   (8-780)

-   -   The predicted luma sample value predSampleLX_(L) is derived as        follows:

predSampleLX _(L)=(Σ_(i=0) ⁷ f _(L) [yFrac_(L) ][i]*temp[i])>>shift2  (8-781)

TABLE 8-11 Specification of the luma interpolation filter coefficientsf_(L)[p] for each 1/16 fractional sample position p. Fractional sampleinterpolation filter coefficients position p f_(L)[p][0] f_(L)[p][1]f_(L)[p][2] f_(L)[p][3] f_(L)[p][4] f_(L)[p][5] f_(L)[p][6] f_(L)[p][7]1 0 1 −3 63 4 −2 1 0 2 −1 2 −5 62 8 −3 1 0 3 −1 3 −8 60 13 −4 1 0 4 −1 4−10 58 17 −5 1 0 5 −1 4 −11 52 26 −8 3 −1 6 −1 3 −9 47 31 −10 4 −1 7 −14 −11 45 34 −10 4 −1 8 −1 4 −11 40 40 −11 4 −1 (hpelIfIdx == 0) 8 0 3 920 20 9 3 0 (hpelIfIdx == 1) 9 −1 4 −10 34 45 −11 4 −1 10 −1 4 −10 31 47−9 3 −1 11 −1 3 −8 26 52 −11 4 −1 12 0 1 −5 17 58 −10 4 −1 13 0 1 −4 1360 −8 3 −1 14 0 1 −3 8 62 −5 2 −1 15 0 1 −2 4 63 −3 1 0

TABLE 8-12 Specification of the luma interpolation filter coefficientsf_(L)[p] for each 1/16 fractional sample position p for affine motionmode. Fractional sample interpolation filter coefficients position pf_(L)[p][0] f_(L)[p][1] f_(L)[p][2] f_(L)[p][3] f_(L)[p][4] f_(L)[p][5]f_(L)[p][6] f_(L)[p][7] 1 0 1 −3 63 4 −2 1 0 2 0 1 −5 62 8 −3 1 0 3 0 2−8 60 13 −4 1 0 4 0 3 −10 58 17 −5 1 0 5 0 3 −11 52 26 −8 2 0 6 0 2 −947 31 −10 3 0 7 0 3 −11 45 34 −10 3 0 8 0 3 −11 40 40 −11 3 0 9 0 3 −1034 45 −11 3 0 10 0 3 −10 31 47 −9 2 0 11 0 2 −8 26 52 −11 3 0 12 0 1 −517 58 −10 3 0 13 0 1 −4 13 60 −8 2 0 14 0 1 −3 8 62 −5 1 0 15 0 1 −2 463 −3 1 0

8.5.6.3.3 Luma Integer Sample Fetching Process

Inputs to this process are:

-   a luma location in full-sample units (xInt_(L), yInt_(L)),-   the luma reference sample array refPicLX_(L),

Output of this process is a predicted luma sample value predSampleLX_(L)

The variable shift is set equal to Max(2, 14−BitDepth_(Y)).

The variable picW is set equal to pic_width_in_luma_samples and thevariable picH is set equal to pic_height_in_luma_samples.

The luma locations in full-sample units (xInt, yInt) are derived asfollows:

xInt=Clip3(0, picW−1, sps_ref_wraparound_enabled_flag?  (8-782)

ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY, picW, xInt_(L)):xInt_(L))

yInt=Clip3(0, picH−1, yInt_(L))   (8-783)

The predicted luma sample value predSampleLX_(L) is derived as follows:

predSampleLX _(L)=refPicLX _(L) [xInt][yInt]<<shift3   (8-784)

8.5.6.3.4 Chroma Sample Interpolation Process

Inputs to this process are:

-   a chroma location in full-sample units (xInt_(C), yint_(C)),-   a chroma location in 1/32 fractional-sample units (xFrac_(C),    yFrac_(C)),-   a chroma location in full-sample units (xSbIntC, ySbIntC) specifying    the top-left sample of the bounding block for reference sample    padding relative to the top-left chroma sample of the reference    picture,-   a variable sbWidth specifying the width of the current subblock,-   a variable sbHeight specifying the height of the current subblock,-   the chroma reference sample array refPicLX_(C).

Output of this process is a predicted chroma sample valuepredSampleLX_(C)

The variables shiftl, shift2 and shift3 are derived as follows:

-   The variable shiftl is set equal to Min(4, BitDepth_(C)−8), the    variable shift2 is set equal to 6 and the variable shift3 is set    equal to Max(2, 14−BitDepth_(C)).-   The variable picW_(C) is set equal to    pic_width_in_luma_samples/SubWidthC and the variable picH_(C) is set    equal to pic_height_in_luma_samples/SubHeightC.

The chroma interpolation filter coefficients f_(C)[p] for each 1/32fractional sample position p equal to xFrac_(C) or yFrac_(C) arespecified in Table 8-13.

The variable xOffset is set equal to(sps_ref_wraparound_offset_minus1+1)*MinCb SizeY)/Sub WidthC.

The chroma locations in full-sample units (xInt_(i), yInt_(i)) arederived as follows for i=0..3:

-   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the    following applies:

xInt_(i)=Clip3 (SubPicLeftBoundaryPos/SubWidthC,SubPicRightBoundaryPos/SubWidthC, xInt_(L) +i)   (8-785)

yInt_(i)=Clip3(SubPicTopBoundaryPos/SubHeightC,SubPicBotBoundaryPos/SubHeightC, yInt_(L) +i)   (8-786)

-   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the    following applies:

xInt_(i)=Clip3(0, picW_(C)−1, sps_ref_wraparound_enabled_flag ?ClipH(xOffset, picW _(C) , xInt_(C) +i−1):   (8-787)

xInt_(C) +i−1) yInt_(i)=Clip3(0, picH _(C)−1, yInt_(C) +i−1)   (8-788)

The chroma locations in full-sample units (xInt_(i), yInt_(i)) arefurther modified as follows for i=0..3:

xInt_(i)=Clip3(xSbIntC−1, xSbIntC+sbWidth+2, xInt_(i))   (8-789)

yInt_(i)=Clip3(ySbIntC−1, ySbIntC+sbHeight+2, yInt_(i))   (8-790)

The predicted chroma sample value predSampleLX_(C) is derived asfollows:

-   If both xFrac_(C) and yFrac_(C) are equal to 0, the value of    predSampleLX_(C) is derived as follows:

predSampleLX _(C)=refPicLX _(C) [xInt₁ ][yInt₁]shift3   (8-791)

-   Otherwise, if xFrac_(C) is not equal to 0 and yFrac_(C) is equal to    0, the value of predSampleLX_(C) is derived as follows:

predSampleLX _(C)=(Σ_(i=0) ³ f _(C) [xFrac_(C) ][i*]refPicLX _(C)[xInt_(i)][yInt₁])>>shift1    (8-792)

-   Otherwise, if xFrac_(C) is equal to 0 and yFrac_(C) is not equal to    0, the value of predSampleLX_(C) is derived as follows:

predSampleLX _(C)=(Σ_(i=0) ³ f _(C) [yFrac_(C) ][i]*refPicLX _(C) [xInt₁][yInt_(i)])>>shift1    (8-793)

-   Otherwise, if xFrac_(C) is not equal to 0 and yFrac_(C) is not equal    to 0, the value of predSampleLX_(C) is derived as follows:    -   The sample array temp[n] with n=0..3, is derived as follows:

temp[n]=(Σ_(i=0) ³ f _(C) [xFrac_(C)][1]*refPicLX _(C) [xInt_(i)][yInt_(n)])>>shift1   (8-794)

-   -   The predicted chroma sample value predSampleLX_(C) is derived as        follows:

predSampleLX _(C)=(f _(C) [yFrac_(C)][0]*temp[0]+f _(C)[yFrac_(C)][1]*temp[1]+f _(C) [yFrac_(C)][2]*temp[2]+f _(C)[yFrac_(C)][3]*temp[3])>>shift2   (8-795)

TABLE 8-13 Specification of the chroma interpolation filter coefficientsf_(C)[ p ] for each 1/32 fractional sample position p. Fractional sampleinterpolation filter coefficients position p f_(C)[ p ][ 0 ] f_(C)[ p ][1 ] f_(C)[ p ][ 2 ] f_(C)[ p ][ 3 ] 1 −1 63 2 0 2 −2 62 4 0 3 −2 60 7 −14 −2 58 10 −2 5 −3 57 12 −2 6 −4 56 14 −2 7 −4 55 15 −2 8 −4 54 16 −2 9−5 53 18 −2 10 −6 52 20 −2 11 −6 49 24 −3 12 −6 46 28 −4 13 −5 44 29 −414 −4 42 30 −4 15 −4 39 33 −4 16 −4 36 36 −4 17 −4 33 39 −4 18 −4 30 42−4 19 −4 29 44 −5 20 −4 28 46 −6 21 −3 24 49 −6 22 −2 20 52 −6 23 −2 1853 −5 24 −2 16 54 −4 25 −2 15 55 −4 26 −2 14 56 −4 27 −2 12 57 −3 28 −210 58 −2 29 −1 7 60 −2 30 0 4 62 −2 31 0 2 63 −1

2.6 Sub-Pictures in JVET-O2001-v14

With the current syntax design of sub-pictures in JVET-O2001-vE, thelocations and dimensions of sub-pictures are derived as below:

subpics_present_flag u(1) if( subpics_present_flag ) { max_subpics_minus1 u(8)  subpic_grid_col_width_minus1 u(v) subpic_grid_row_height_minus1 u(v)  for( i = 0; i < NumSubPicGridRows;i++ )   for( j = 0; j < NumSubPicGridCols; j++ )    subpic_grid_idx[ i][ j ] u(v)  for( i = 0; i <= NumSubPics; i++ ) {  subpic_treated_as_pic_flag[ i ] u(1)  loop_filter_across_subpic_enabled_flag[i ] u(1)  } }

-   subpics_present_flag equal to 1 indicates that subpicture parameters    are present in the present in the SPS RBSP syntax.    subpics_present_flag equal to 0 indicates that subpicture parameters    are not present in the present in the SPS RBSP syntax.

When a bitstream is the result of a sub-bitstream extraction process andincludes only a subset of the subpictures of the input bitstream to thesub-bitstream extraction process, it might be required to set the valueof subpics_present_flag equal to 1 in the RBSP of the SPSs.

-   max_subpics_minus1 plus 1 specifies the maximum number of    subpictures that may be present in the CVS. max_subpics_minus1 shall    be in the range of 0 to 254. The value of 255 is reserved for future    use by ITU-T|ISO/IEC.-   subpic_grid_col_width_minus1 plus 1 specifies the width of each    element of the subpicture identifier grid in units of 4 samples. The    length of the syntax element is Ceil(Log    2(pic_width_max_in_luma_samples/4)) bits.

The variable NumSubPicGridCols is derived as follows:

NumSubPicGridCols=(pic_width_max_in_luma_samples+subpic_grid_col_width_minus1*4+3)/(subpic_grid_col_width_minus1*4+4)  (7-5)

-   subpic_grid_row_height_minus1 plus 1 specifies the height of each    element of the subpicture identifier grid in units of 4 samples. The    length of the syntax element is Ceil(Log    2(pic_height_max_in_luma_samples/4)) bits.

The variable NumSubPicGridRows is derived as follows:

NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1*4+3)/(subpic_grid_row_height_minus1*4+4)  (7-6)

-   subpic_grid_idx[i][j] specifies the subpicture index of the grid    position (i, j). The length of the syntax element is Ceil(Log    2(max_subpics_minus1+1)) bits.

The variables SubPicTop[subpic_grid_idx[i][j]],SubPicLeft[subpic_grid_idx[i][j]], SubPicWidth[subpic_grid_idx [i][j]],SubPicHeight[subpic_grid_idx[i][j]], and NumSubPics are derived asfollows:

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) {  for( j = 0;j < NumSubPicGridCols; j++ ) {   if ( i = = 0)     SubPicTop[subpic_grid_idx[ i ][ j ] ] = 0   else if( subpic_grid_idx[ i ][ j ] !=subpic_grid_idx[ i − 1 ][ j ] ) {     SubPicTop[ subpic_grid_idx[ i ][ j] ] = i    SubPicHeight[ subpic_grid_idx[ i − 1 ][ j ] ] = i −SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ]   }   if ( j = = 0)    SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0     (7-7)   else if(subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) {    SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j     SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ]   }   if( i = = NumSubPicGridRows − 1)     SubPicHeight[subpic_grid_idx[ i ][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j] ] + 1   if (j = = NumSubPicGridRows − 1)     SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ] + 1   if( subpic_grid_idx[ i ][ j ] > NumSubPics)      NumSubPics= subpic_grid_idx[ i ][ j ]  } }

-   subpic_treated_as_pic_flag[i] equal to 1 specifies that the i-th    subpicture of each coded picture in the CVS is treated as a picture    in the decoding process excluding in-loop filtering operations.    subpic_treated_as_pic_flag[i] equal to 0 specifies that the i-th    subpicture of each coded picture in the CVS is not treated as a    picture in the decoding process excluding in-loop filtering    operations. When not present, the value of    subpic_treated_as_pic_flag[i] is inferred to be equal to 0.

2.7 CIIP in JVET-O2001-v14

Combined Inter-Intra Prediction (CIIP) is adopted into VVC as a specialmerge candidate. It can only be enabled for a W×H block with W<=64 andH<=64.

3. Examples of Problems Solved by Disclosed Techniques and Embodiments

In the current design of VVC, ATMVP has following problems:

-   -   1) Whether to apply ATMVP is mismatched in slice level and in CU        level;    -   2) In slice header, ATMVP may be enabled even if TMVP is        disabled. Meanwhile, ATMVP flag is signaled before TMVP flag.    -   3) Masking is always done without considering whether MV is        compressed;    -   4) The valid corresponding region may be too large;    -   5) The derivation of TMV is too complicated;    -   6) ATMVP may be unavailable in some cases and a better default        MV is desirable.    -   7) The MV scaling methods in ATMVP may not be efficient;    -   8) ATMVP should consider the CPR cases;    -   9) A default zero affine merge candidate may be put into the        list even when affineprediction is disabled.    -   10) Current picture is treated as a long-term reference picture        while other pictures are treated as short-reference picture. For        both ATMVP and TMVP candidates, the motion information from a        temporal block in the collocated picture will be scaled to a        reference picture with fixed reference index (i.e., 0 for each        reference picture list in the current design). However, when CPR        mode is enabled, the current picture is also treated as a        reference picture and the current picture may be added to the        reference picture list 0 (RefPicList0) with index equal to 0.        -   a. For TMVP, if the temporal block is coded with CPR mode            and reference picture of RefPicListO is a short reference            picture, the TMVP candidate is set to be unavailable.        -   b. If the reference picture of the RefPicListO with index            equal to 0 is the current picture and current picture is the            Intra Random Access Point (IRAP) picture, ATMVP candidate is            set to be unavailable.        -   c. For a ATMVP sub-block within a block, when deriving the            sub-block's motion information from a temporal block, if the            temporal block is coded with CPR mode, default ATMVP            candidate (derived from a temporal block identified by the            starting TMV and center position of the current block) is            used to fill in the sub-block′ motion information.    -   11) MV is right shifted to the integer precision, but not        following the rounding rule in VVC.    -   12) The MV(MVx, MVy) used in ATMVP to locate a corresponding        block in a different picture (e.g., the TMV in 2.3.5.1.2) is        directly used since it points to the collocated picture. This is        based on the assumption that all pictures are in the same        resolution. However, when RPR is enabled, different picture        resolutions may be utilized. Similar issues are existing for        identification of corresponding blocks in a collocate picture to        derive sub-block motion information.    -   13) If one block width or height is greater than 32, and max        transform unit size is 32, for a CIIP coded block, the intra        prediction signal is generated with the coding unit (CU) size;        while the inter prediction signal is generated with the        transform unit (TU) size (recursively splitting current block to        multiple 32×32 blocks). Using the CU to derive intra prediction        signal results in less efficiency.

There are some problems with current design. Firstly, if the referencepicture of the RefPicList0 with index equal to 0 is the current pictureand current picture is not an TRAP picture, ATMVP procedure is stillinvoked, but the ATMVP procedure cannot locate any available ATMVPcandidates since none of temporal motion vectors can be scaled to thecurrent picture.

4. Examples of Embodiments and Techniques

The itemized list of techniques and embodiments below should beconsidered as examples to explain general concepts. These techniquesshould not be interpreted in a narrow way. Furthermore, these techniquescan be combined in any manner in encoder or decoder embodiments.

-   1. Whether TMVP is allowed and/or whether CPR is used should be    considered to decide/parse the maximum number of candidates in the    sub-block merge candidate list and/or to decide whether ATMVP    candidate should be added to a candidate list. The maximum number of    candidates in the sub-block merge candidate list is denoted as ML.    Although some of the example embodiments are discussed below using    alternative temporal motion vector prediction (ATMVP), in alternate    embodiments, the technology disclosed in this document is applicable    to sub-block based temporal motion vector prediction (sbTMVP).    -   a) In one example, ATMVP is inferred to be not applicable if        either ATMVP usage flag is off (equal to 0), or TMVP is        disabled, in the determination of or parsing the maximum number        of candidates in the sub-block merge candidate list.        -   i. In one example, the ATMVP usage flag is on (equal to 1)            and TMVP is disabled, the ATMVP candidate is not added to            the sub-block merge candidate list or the ATMVP candidate            list.        -   ii. In one example, the ATMVP usage flag is on (equal to 1)            and TMVP is disabled, and the affine usage flag is off            (equal to 0), then ML is set equal to 0, meaning that            sub-block merge is not applicable.        -   iii. In one example, the ATMVP usage flag is on (equal to 1)            and TMVP is enabled, and the affine usage flag is off (equal            to 0), then ML is set equal to 1.    -   b) In one example, ATMVP is inferred to be not applicable if        either ATMVP usage flag is off (equal to 0), or the collocated        reference picture of the current picture is the current picture        itself, when decide or parse the maximum number of candidates in        the sub-block merge candidate list.        -   i. In one example, the ATMVP usage flag is on (equal to 1)            and the collocated reference picture of the current picture            is the current picture itself, the ATMVP candidate is not            added to the sub-block merge candidate list or the ATMVP            candidate list.        -   ii. In one example, the ATMVP usage flag is on (equal to 1),            and the collocated reference picture of the current picture            is the current picture itself, and the affine usage flag is            off (equal to 0), then ML is set equal to 0, meaning that            sub-block merge is not applicable.        -   iii. In one example, the ATMVP usage flag is on (equal to            1), and the collocated reference picture ofthe current            picture is not the current picture itself, and the affine            usage flag is off (equal to 0), then ML is set equal to 1.    -   c) In one example, ATMVP is inferred to be not applicable if        ATMVP usage flag is off (equal to 0), or the reference picture        with reference picture index 0 in reference list 0 is the        current picture itself, when decide or parse the maximum number        of candidates in the sub-block merge candidate list.        -   i. In one example, the ATMVP usage flag is on (equal to 1)            and the collocated reference picture with reference picture            index 0 in reference list 0 is the current picture itself,            the ATMVP candidate is not added to the sub-block merge            candidate list or the ATMVP candidate list.        -   ii. In one example, the ATMVP usage flag is on (equal to 1),            and the reference picture with reference picture index 0 in            reference list 0 is the current picture itself, and the            affine usage flag is off (equal to 0), then ML is set equal            to 0, meaning that sub-block merge is not applicable.        -   iii. In one example, the ATMVP usage flag is on (equal to 1)            and the reference picture with reference picture index 0 in            reference list 0 is not the current picture itself, and the            affine usage flag is off (equal to 0), then ML is set equal            to 1.    -   d) In one example, ATMVP is inferred to be not applicable if        ATMVP usage flag is off (equal to 0), or the reference picture        with reference picture index 0 in reference list 1 is the        current picture itself, when decide or parse the maximum number        of candidates in the sub-block merge candidate list.        -   i. In one example, the ATMVP usage flag is on (equal to 1)            and the collocated reference picture with reference picture            index 0 in reference list 1 is the current picture itself,            the ATMVP candidate is not added to the sub-block merge            candidate list or the ATMVP candidate list.        -   ii. In one example, the ATMVP usage flag is on (equal to 1),            and the reference picture with reference picture index 0 in            reference list 1 is the current picture itself, and the            affine usage flag is off (equal to 0), then ML is set equal            to 0, meaning that sub-block merge is not applicable.        -   iii. In one example, the ATMVP usage flag is on (equal to 1)            and the reference picture with reference picture index 0 in            reference list 1 is not the current picture itself, and the            affine usage flag is off (equal to 0), then ML is set equal            to 1.-   2. It is proposed that ATMVP is disabled implicitly and no ATMVP    flag is signaled if TMVP is disabled at slice/tile/picture level.    -   a) In one example, ATMVP flag is signaled after the TMVP flag in        slice header/tile header/PPS.    -   b) In one example, ATMVP or/and TMVP flag may be not signaled in        slice header/tile header/PPS and is only signaled in SPS header.-   3. Whether and how to do mask the corresponding position in ATMVP    depends on whether and how MVs are compressed. Suppose (xN, yN) is a    corresponding position calculated with the coordinator of current    block/sub-block and a starting motion vector (e.g., TMV) in the    collocated picture    -   a) In one example, (xN, yN) is not masked if MVs are not        required to be compressed (e.g. sps_disable_motioncompression        signaled in SPS is 1); Otherwise, (MVs can be compressed) (xN,        yN) is masked as xN=xN&MASK, yN=yN& MASK, where MASK is an        integer equal to ˜(2^(M)−1), and M can be integers such as 3 or        4.    -   b) Assume the MV compression method for MV storage result in        each 2^(K)×2^(K) block share the same motion information and the        mask in the ATMVP process is defined as ˜(2^(M)−1). It is        proposed that K may be unequal to M, e.g., M=K+1.    -   c) The MASK used in ATMVP and TMVP may be the same, or they may        be different.-   4. In one example, the MV compression method can be flexible.    -   a) In one example, the MV compression method can be selected        between no compression, 8×8 compression (M=3 in Bullet 3.a), or        16 ×16 compression (M=4 in Bullet 3.a)    -   b) In one example, the MV compression method may be signaled in        VPS/SPS/PPS/slice header/tile group header.    -   c) In one example, the MV compression method can be set        differently in different standard profiles/levels/tiers.-   5. The valid corresponding region in ATMVP may adaptive;    -   a) For example, the valid corresponding region may depend on the        width and height of the current block;    -   b) For example, the valid corresponding region may depend on the        MV compression method;        -   i. In one example, the valid corresponding region is smaller            if MV compression method is not used; the valid            corresponding region is larger if MV compression method is            used.-   6. The valid corresponding region in ATMVP may be based on a basic    region with size M×N smaller than a CTU region. For example, the CTU    size in VTM-3 .0 is 128 ×128, and the basic region size may be    64×64. Suppose the width and height of the current block is W and H.    -   a) In one example, if W<=M and H<=N, meaning that the current        block is inside a basic region, then the valid corresponding        region in ATMVP is the collocated basic region and the extension        in the collocated picture. FIG. 27 shows an example.        -   i. For example, suppose the top-left position of the            collocated basic region is (xBR, yBR), then the            corresponding position at (xN, yN) will be clipped into the            valid region xBR<=xN<xBR+M+4; yBR<=yN<yBR+N.

FIG. 27 shows an example embodiment of the proposed valid region whenthe current block is inside a Basic Region (BR).

FIG. 28 shows an example embodiment of a valid region when the currentblock is not inside a basic region.

-   -   b) In one example, if W>M and H>N, meaning that the current        block is not inside a basic region, then the current block is        divided into several parts. Each part has an individual valid        corresponding region in ATMVP. For a position A in the current        block, its corresponding position B in the collocated block        should be within the valid corresponding region of the part in        which the positionA locates.        -   i. For example, the current block is divided into            non-overlapped basic regions. The valid corresponding region            for one basic region is its collocated basic region and the            extension in the collocated picture. FIG. 28 shows an            example.            -   1. For example, suppose position A in the current block                is in one basic region R. The collocated basic region of                R in the collocated picture is denoted as CR. The                corresponding position of A in the collocated block is                position B. The top-left position of CR is (xCR, yCR),                then position B at (xN, yN) will be clipped into the                valid region xCR<=xN<xCR+M+4; yCR<=yN<yCR+N.

-   7. It is proposed the motion vector used in ATMVP to locate a    corresponding block in a different picture (e.g., the TMV in    2.3.5.1.2) can be derived as:    -   a) In one example, TMV is always set equal to a default MV such        as (0, 0).        -   i. In one example, the default MV is signaled in            VPS/SPS/PPS/slice header/tile group header/CTU/CU.    -   b) In one example, TMV is set to be one MV stored in the HMVP        table with the following methods;        -   i. If HMVP list is empty, TMV is set equal to a default MV            such as (0, 0)        -   ii. Otherwise (HMVP list is not empty),            -   1. TMV may be set to equal to the first element stored                in the HMVP table;            -   2. Alternatively, TMV may be set to equal to the last                element stored in the HMVP table;            -   3. Alternatively, TMV may only be set equal to a                specific MV stored in the HMVP table;                -   a. In one example, the specific MV refers to                    reference list 0.                -   b. In one example, the specific MV refers to                    reference list 1.                -   c. In one example, the specific MV refers to a                    specific reference picture in reference list 0, such                    as the reference picture with index 0.                -   d. In one example, the specific MV refers to a                    specific reference picture in reference list 1, such                    as the reference picture with index 0.                -   e. In one example, the specific MV refers to the                    collocated picture.            -   4. Alternatively, TMV may be set equal to the default MV                if the specific MV (e.g., mentioned in bullet 3.) stored                in the HMVP table cannot be found;                -   a. In one example, only the first element stored in                    the HMVP table is searched to find the specific MV.                -   b. In one example, only the last element stored in                    the HMVP table is searched to find the specific MV.                -   c. In one example, some or all elements stored in                    the HMVP table is searched to find the specific MV.            -   5. Alternatively, furthermore, TMV obtained from the                HMVP cannot refer to the current picture itself.            -   6. Alternatively, furthermore, TMV obtained from the                HMVP table may be scaled to the collocated picture if it                does not refer to it.    -   c) In one example, TMV is set to be one MV of one specific        neighbouring block. No other neighbouring blocks are involved.        -   i. The specific neighbouringblock may be block A0, A1, B0,            B1, B2 in FIG. 22.        -   ii. TMV may be set equal to the default MV if            -   1. The specific neighbouring block does not exist;            -   2. The specific neighbouring block is not inter-coded;        -   iii. TMV may only be set equal to a specific MV stored in            the specific neighbouring block;            -   1. In one example, the specific MV refers to reference                list 0.            -   2. In one example, the specific MV refers to reference                list 1.            -   3. In one example, the specific MV refers to a specific                reference picture in reference list 0, such as the                reference picture with index 0.            -   4. In one example, the specific MV refers to a specific                reference picture in reference list 1, such as the                reference picture with index 0.            -   5. In one example, the specific MV refers to the                collocated picture.            -   6. TMV may be set equal to the defaultMV if the specific                MV stored in the specific neighbouring block cannot be                found;        -   iv. TMV obtained from the specific neighbouring block may be            scaled to the collocated picture if it does not refer to it.        -   v. TMV obtained from the specific neighbouring block cannot            refer to the current picture itself.

-   8. MVdefault0 and MVdefault1 used in ATMVP as disclosed in 2.3.5.1.2    may be derived as    -   a) In one example, MVdefault0 and MVdefault1 are set equal to        (0,0);    -   b) In one example, MVdefaultX (X=0 or 1) is derived from HMVP,        -   i. If HMVP list is empty, MVdefaultX is set equal to a            predefined default MV such as (0, 0).            -   1. The predefined default MV may be signaled in                VPS/SPS/PPS/slice header/tile group header/CTU/CU.        -   ii. Otherwise (HMVP list is not empty),            -   1. MVdefaultX may be set to equal to the first element                stored in the HMVP table;            -   2. MVdefaultX may be set to equal to the last element                stored in the HMVP table;            -   3. MVdefaultX may only be set equal to a specific MV                stored in the HMVP table;                -   a. In one example, the specific MV refers to                    reference list X.                -   b. In one example, the specific MV refers to a                    specific reference picture in reference list X, such                    as the reference picture with index 0.            -   4. MVdefaultX may be set equal to the predefined default                MV if the specific MV stored in the HMVP table cannot be                found;                -   a. In one example, only the first element stored in                    the HMVP table is searched.                -   b. In one example, only the last element stored in                    the HMVP table is searched.                -   c. In one example, some or all elements stored in                    the HMVP table is searched.            -   5. MVdefaultX obtained from the HMVP table may be scaled                to the collocated picture if it does not refer to it.            -   6. MVdefaultX obtained from the HMVP cannot refer to the                current picture itself.    -   c) In one example, MVdefaultX (X=0 or 1) is derived from a        neighbouring block.        -   i. The neighbouring blocks may include block A0, A1, B0, B1,            B2 in FIG. 22.            -   1. For example, only one of these blocks is used to                derive MVdefaultX.            -   2. Alternatively, some or all of these blocks are used                to derive MVdefaultX.                -   a. These blocks are checked in order until a valid                    MVdefaultX is found.            -   3. If no valid MVdefaultX can be found from selected one                or more neighbouring blocks, it is set equal to a                predefined default MV such as (0, 0).                -   a. The predefined default MV may be signaled in                    VPS/SPS/PPS/slice header/tile group header/CTU/CU.        -   ii. No valid MVdefaultX can be found from a specific            neighbouring block if            -   1. The specific neighbouring block does not exist;            -   2. The specific neighbouring block is not inter-coded;        -   iii. MVdefaultX may only be set equal to a specific MV            stored in the specific neighbouring block;            -   1. In one example, the specific MV refers to reference                list X.            -   2. In one example, the specific MV refers to a specific                reference picture in reference list X., such as the                reference picture with index 0        -   iv. MVdefaultX obtained from the specific neighbouring block            may be scaled to a specific reference picture, such as the            reference picture with index 0 in reference list X.        -   v. MVdefaultX obtained from the specific neighbouring block            cannot refer to the current picture itself.

-   9. For either sub-block or non-sub-block ATMVP candidate, if a    temporal block for a sub-block/whole block in the collocated picture    is coded with CPR mode, a default motion candidate may be utilized    instead.    -   a) In one example, the default motion candidate may be defined        as the motion candidate associated with the center position of        current block (e.g., MVdefault0 and/or MVdefault1 used in ATMVP        as disclosed in 2.3.5.1.2).    -   b) In one example, the default motion candidate may be defined        as (0, 0) motion vector and reference picture index equal to 0        for both reference picture lists, if available.

-   10. It is proposed that the default motion information for the ATMVP    process (e.g., MVdefault0 and MVdefault1 used in ATMVP as disclosed    in 2.3.5.1.2) may be derived based on the location of a position    that is used in the sub-block motion information derivation process.    With this proposed method, for that sub-block, there is no need to    further derive motion information since the default motion    information will be directly assigned.    -   a) In one example, instead of using the center position of the        current block, the center position of a sub-block (e.g., a        center sub-block) within the current block may be utilized.    -   b) An example is given as depicted in FIG. 31B. FIG. 31A shows        an example of locations for identification of default motion        information in the current standards.

-   11. It is proposed that the ATMVP candidate is always available with    the following methods:    -   a) Suppose the center point of the current block is (x0, y0),        then locate a corresponding position of (x0,y0) as M=(x0+MV′x,        y0+MV′y) in the collocated picture. Find the block Z covering M.        If Z is intra-coded, then MVdefault0, MVdefault1 are derived by        some methods proposed in Item 6.    -   b) Alternatively, Block Z is not located to get the motion        information, somemethods proposed in Item 8 are directly applied        to get MVdefault0 and MVdefault1.    -   c) Alternatively, the default motion candidate used in ATMVP        process is always available. If it is set to unavailable based        on current design (e.g., the temporal block is intra coded),        other motion vectors may be utilized instead for the default        motion candidate.        -   i. In one example, the solutions in international            application PCT/CN2018/124639, incorporated by reference            herein, may be applied.    -   d) Alternatively, furthermore, whether ATMVP candidate is always        available depend on other high-level syntax information.        -   i. In one example, only when the ATMVP enabling flag at            slice/tile/picture header or other video units is set to            true is inferred to be true, the ATMVP candidate may be            always set to be available.        -   ii. In one example, the ab ove methods may be only            applicable when ATMVP enabling flag in slice header/picture            header or other video units is set to true and current            picture is not an TRAP picture and current picture is not            inserted to RefPicListO with reference index equal to 0.        -   e) A fixed index or a fixed group of indices is assigned to            ATMVP candidates. When ATMVP candidates are always            unavailable, the fixed index/group index may be inferred to            other kinds of motion candidates (such as affine            candidates).

-   12. It is proposed that whether the Zero motion affine merge    candidate is put into the sub-block merge candidate list should    depend on whether affine prediction is enabled.    -   a) For example, if affine usage flag is off        (sps_affine_enabled_flag is equal to 0), the Zero motion affine        merge candidate is not put into the sub-block merge candidate        list.    -   b) Alternatively, furthermore, default motion vector candidates        which are non-affine candidate are added instead.

-   13. It is proposed that non-affine padding candidate may be put into    the sub-block merge candidate list.    -   a) Zero motion non-affine padding candidate may be added if the        sub-block merge candidate list is not fulfilled.    -   b) When such a padding candidate is chosen, the affine flag of        the current block should be set to be 0.    -   c) Alternatively, Zero motion non-affine padding candidate is        put into the sub-block merge candidate list if the sub-block        merge candidate list is not fulfilled and affine usage flag is        off.

-   14. Suppose MV0 and MV1 represent the MVs in reference list 0 and    reference list 1 of the block covering a corresponding position    (e.g., MV0 and MV1 may be MVZ_0 and MVZ_1 or MVZS_0 and MVZS_1    described in section 2.3.5.1.2). MV0′ and MV1′ represent the MVs in    reference list 0 and reference list 1 to be derived for the current    block or sub-block. Then the MV0′ and MV1′ should be derived by    scaling.    -   a) MV0, if the collocated picture is in reference list 1;    -   b) MV1, if the collocated picture is in reference list 0.

-   15. The ATMVP and/or TMVP enabling/disabling flag may be inferred to    be false for a slice/tile or other kinds of video units when current    picture is treated as a reference picture with index set to M    (e.g., 0) in a reference picture list X (PicRefListX, e.g., X=0).    Here, M may be equal to the target reference picture index that    motion information of a temporal block shall be scaled to for    PicRefListX during ATMVP/TMVP processes.    -   a) Alternatively, furthermore, the above method is only        applicable when the current picture is an Intra Random Access        Point (IRAP) picture.    -   b) In one example, ATMVP and/or TMVP enabling/disabling flag may        be inferred to be false when current picture is treated as a        reference picture with index set to M (e.g., 0) in a PicRefListX        and/or current picture is treated as a reference picture with        index set to N (e.g., 0) in a PicRefListY. The variable M and N        represent the target reference picture index used in TMVP or        ATMVP process.    -   c) For the ATMVP process, it is restricted that a confirming        bitstream shall follow the rule that the collocated picture        wherein motion information of current block is derived from        shall not be the current picture.    -   d) Alternatively, when the above conditions are true, the ATMVP        or TMVP process is not invoked.

-   16. It is proposed that if a reference picture with index set to M    (e.g., 0) in a reference picture list X (PicRefListX, e.g., X=0) for    the current block is the current picture, ATMVP may be still enabled    for this block.    -   a) In one example, all sub-blocks' motion information are point        to the current picture.    -   b) In one example, when obtaining the sub-block's motion        information from a temporal block, the temporal block shall be        coded with at least one reference picture pointing to the        current picture of the temporal block.    -   c) In one example, when obtaining the sub-block's motion        information from a temporal block, no scaling operations are        applied.

-   17. Coding methods of sub-block merge index are aligned regardless    the usage of ATMVP or not.    -   a) In one example, for the first L bins, they are context coded.        For the remaining bins, they are bypass coded. In one example, L        is set to 1.    -   b) Alternatively, for all bins, they are context coded.

-   18. The MV(MVx, MVy) used in ATMVP to locate a corresponding block    in a different picture (e.g., the TMV in 2.3.5.1.2) may be    right-shifted to the integer precision (denoted as (MVx′, MVy′) with    the same rounding method as in the MV scaling process.    -   a) Alternatively, the MV used in ATMVP to locate a corresponding        block in a different picture (e.g., the TMV in 2.3.5.1.2) may be        right-shifted to the integer precision with the same rounding        method as in the MV averaging process.    -   b) Alternatively, the MV used in ATMVP to locate a corresponding        block in a different picture (e.g., the TMV in 2.3.5.1.2) may be        right-shifted to the integer precision with the same rounding        method as in the adaptive MV resolution (AMVR) process.

-   19. The MV(MVx, MVy) used in ATMVP to locate a corresponding block    in a different picture (e.g., the TMV in 2.3.5.1.2) may be    right-shifted to the integer precision (denoted as (MVx′, MVy′) by    rounding toward zero.    -   a) For example, MVx′=(MVx+((1<<N)>>1)−(MVx>=0? 1:0))>>N; N is an        integer presenting the MV resolution, e.g. N=4.        -   i. For example, MVx′=(MVx+(MVx>=0 ? 7:8))>>4.    -   b) For example, MVy′=(MVy+((1<<N)>>1)−(MVy>=0? 1:0))>>N; N is an        integer presenting the MV resolution, e.g. N=4.        -   i. For example, MVy′=(MVy+(MVy>=0 ? 7:8))>>4.

-   20. In one example, MV(MVx, MVy) in bullet 18 and bullet 19 is used    to locate a corresponding block to derive the default motion    information used in ATMVP, such as using the center position of the    sub-block and the shifted MV, or using the top-left position of    current block and the shifted MV.    -   a) In one example, MV(MVx, MVy) is used to locate a        corresponding block to derive the motion information of a        sub-block in currentblock duringthe ATMVP process, such as using        the center position of the sub-block and the shifted MV.

-   21. The proposed methods in bullet 18, 19, 20 may be also applied to    other coding tools associated with locating a reference block in a    different picture or current picture with a motion vector.

-   22. The MV(MVx, MVy) used in ATMVP to locate a corresponding block    in a different picture (e.g., the TMV in 2.3.5.1.2) may be scaled    even if it points to the collocated picture.    -   a) In one example, if the width and/or height of the collocated        picture (or the conformance window in it) is different from that        of the current picture (or the conformance window in it), the MV        may be scaled.    -   b) Suppose the width and height of (the conformance window) of        the collocated picture are denoted as W1 and H1, respectively.        The width and height of (the conformance window of) the current        picture are denoted as W2 and H2, respectively. Then MV(MVx,        MVy) may be scaled as MVx′=MVx*W1/W2 and MVy′=MVy*H1/H2.

-   23. The center point of the currentblock (such as position (x0, y0)    in 2.3.5.1.2) used to derive motion information in the ATMVP process    may be further modified by scaling and/or adding offsets.    -   a) In one example, if the width and/or height of the collocated        picture (or the conformance window in it) is different from that        of the current picture (or the conformance window in it), the        center point may be further modified.    -   b) Suppose the top-left position of the conformance window in        the collocated picture are denoted as X1 and Y1. The top-left        position of the conformance window defined in the current        picture are denoted as X2 and Y2. The width and height of (the        conformance window of) the collocated picture are denoted as W1        and H1, respectively. The width and height of (the conformance        window) of the current picture are denoted as W2 and H2,        respectively. Then (x0, y0) may be modified as        x0′=(x0−X2)*W1/W2+×1 and y0′=(y0−Y2)*H1/H2+Y1.        -   i. Alternatively, x0′=x0*W1/W2, y0′=y0*H1/H2.

-   24. The corresponding position (such as position M in 2.3.5.1.2)    used to derive motion information in the ATMVP process may be    further modified by scaling and/or adding offsets    -   a) In one example, if the width and/or height of the collocated        picture (or the conformance window in it) is different from that        of the current picture (or the conformance window in it), the        corresponding position may be further modified.    -   b) Suppose the top-left position of the conformance window in        the collocated picture are denoted as X1 and Y1. The top-left        position of the conformance window defined in the current        picture are denoted as X2 and Y2. The width and height of (the        conformance window of) the collocated picture are denoted as W1        and H1, respectively. The width and height of (the conformance        window) of the current picture are denoted as W2 and H2,        respectively. Then M(x, y) may be modified as x′=(x−X2)*W1/W2+X        1 and y′=(y−Y2)*H1/H2+Y1.        -   i. Alternatively, x′=x*W1/W2, y′=y*H1/H2.

Sub-Picture Related

-   25. In one example, the width of a sub-picture S ending at the (j−1)    column may be set equal to j minus the left-most column of the    sub-picture S, if the position (i, j) and (i, j−1) belong to    different sub-pictures.    -   a) An embodiment based on JVET-O2001-vE is highlighted below in        bold, italicized font.

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) {  for( j = 0;j < NumSubPicGridCols; j++ ) {   if ( i = = 0)     SubPicTop[subpic_grid_idx[ i ][ j ] ] = 0   else if( subpic_grid_idx[ i ][ j ] !=subpic_grid_idx[ i − 1 ][ j ] ) {     SubPicTop[ subpic_grid_idx[ i ][ j] ] = i    SubPicHeight[ subpic_grid_idx[ i − 1][ j ] ] = i − SubPicTop[subpic_grid_idx[ i − 1 ][ j ] ]   }   if ( j = = 0)     SubPicLeft[subpic_grid_idx[ i ][ j ] ] = 0    (7-7)   else if (subpic_grid_idx[ i][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) {     SubPicLeft[subpic_grid_idx[ i ][ j ] ] = j     

   

    }   if( i = = NumSubPicGridRows − 1)     SubPicHeight[subpic_grid_idx[ i ][ j ] ] = i − SubPicTop[ subpic_grid_idx[ i − 1 ][ j] ] + 1   if (j = = NumSubPicGridRows − 1)     SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ] + 1   if( subpic_grid_idx[ i ][ j ] > NumSubPics)     NumSubPics =subpic_grid_idx[ i ][ j ]  } }

-   26. In one example, the height of a sub-picture S ending at the    (NumSubPicGridRows−1) row may be set equal to (NumSubPicGridRows−1)    minus the top-most row of the sub-picture S then plus one.    -   a) An embodiment based on JVET-O2001-vE is highlighted below.

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) {  for( j = 0;j < NumSubPicGridCols; j++ ) {   if ( i = = 0)     SubPicTop[subpic_grid_idx[ i ][ j ] ] = 0   else if( subpic_grid_idx[ i ][ j ] !=subpic_grid_idx[ i − 1 ][ j ] ) {     SubPicTop[ subpic_grid_idx[ i ][ j] ] = i     SubPicHeight[ subpic_grid_idx[ i − 1][ j ] ] = i −SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ]   }   if ( j = = 0)    SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = 0    (7-7)   else if(subpic_grid_idx[ i ][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) {    SubPicLeft[ subpic_grid_idx[ i ][ j ] ] = j     SubPicWidth[subpic_grid_idx[ i ][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j −1 ] ]   }   if( i = = NumSubPicGridRows − 1)      

   

    if (j = = NumSubPicGridRows − 1)     SubPicWidth[ subpic_grid_idx[ i][ j ] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ] + 1   if(subpic_grid_idx[ i ][ j ] > NumSubPics)     NumSubPics =subpic_grid_idx[ i ][ j ]

-   27. In one example, the width of a sub-picture S ending atthe (Num    SubPicGridColumns−1) column may be set equal to (Num    SubPicGridColumns−1) minus the left-most column of the sub-picture S    then plus 1.    -   a) An embodiment based on JVET-O2001-vE is highlighted below.

NumSubPics = 0 for( i = 0; i. < NumSubPicGridRows; i++ ) {  for( j = 0;j < NumSubPicGridCols; j++ ) {   if ( i = = 0)    SubPicTop[subpic_grid_idx[ i ][ j ] ] = 0   else if( subpic_grid_idx[ i ][ j ] !=subpic_grid_idx[ i − 1 ][ j ] ) {    SubPicTop[ subpic_grid_idx[ i ][ j] ] = i    SubPicHeight[ subpic_grid_idx[ i − 1][ j ] ] = i − SubPicTop[subpic_grid_idx[ i − 1 ][ j ] ]   }   if ( j = = 0)    SubPicLeft[subpic_grid_idx[ i ][ j ] ] = 0     (7-7)   else if (subpic_grid_idx[ i][ j ] != subpic_grid_idx[ i ][ j − 1 ] ) {    SubPicLeft[subpic_grid_idx[ i ][ j ] ] = j    SubPicWidth[ subpic_grid_idx[ i ][ j] ] = j − SubPicLeft[ subpic_grid_idx[ i ][ j − 1 ] ]   }   if( i = =NumSubPicGridRows − 1)    SubPicHeight[ subpic_grid_idx[ i ][ j ] ] = i− SubPicTop[ subpic_grid_idx[ i − 1 ][ j ] ] + 1    

      

   

    if( subpic_grid_idx[ i ][ j ] > NumSubPics)    NumSubPics =subpic_grid_idx[ i ][ j ]

-   28. The sub-picture grid can be integer times of the CTU size.    -   a) An embodiment based on JVET-O2001-vE is highlighted below-   subpic_grid_col_width_minus1 plus 1 specifies the width of each    element of the subpicture identifier grid in units of CtbSizeY. The    length of the syntax element is Ceil(Log    2(pic_width_max_in_luma_samples/CtbSizeY)) bits.

The variable NumSubPicGridCols is derived as follows:

NumSubPicGridCols=(pic_width_max_in_luma_samples+subpic_grid_col_width_minus1*CtbSizeY+CtbSizeY−1)/(subpic_grid_col_width_minus1*CtbSizeY+CtbSizeY)  (7-5)

-   subpic_grid_row_height_minus1 plus 1 specifies the height of each    element of the subpicture identifier grid in units of 4 samples. The    length of the syntax element is Ceil(Log    2(pic_height_max_in_luma_samples/CtbSizeY)) bits.

The variable NumSubPicGridRows is derived as follows:

NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1*CtbSizeY+CtbSizeY−1)/(subpic_grid_row_height_minus1*CtbSizeY+CtbSizeY)  (7-6)

-   29. A conformance constraint is added to guarantee that sub-pictures    cannot be overlapped with each other, and all the sub-pictures can    cover the whole picture.    -   a) An embodiment based on JVET-O2001-vE is indicated below.

Any subpic grid_idx[i][j] must be equal to idx if the followingconditions are both satisfied:

i>=SubPicTop[idx] and i<SubPicTop[idx]+SubPicHeight[idx].

j>=SubPicLeft[idx] and j<SubPicLeft[idx]+SubPicWidth[idx].

Any subpic_grid_idx[i][j] must be different to idx if the followingconditions are not both satisfied:

i>=SubPicTop[idx] and i<SubPicTop[idx]+SubPicHeight[idx].

j>=SubPicLeft[idx] and j<SubPicLeft[idx]+SubPicWidth[idx].

RPR Related

-   30. A syntax element (such as a flag), denoted as RPR_flag, is    signaled to indicate whether RPR may be used or not in a video unit    (e.g., sequence). RPR_flag may be signaled in SPS, VPS, or DPS.    -   a) In one example, if RPR is signaled not to be used (e.g.        RPR_flag is 0) all width/height signaled in picture parameter        set (PPS) can be the same to the maximum width/maximum height        signaled in sequence parameter set (SPS).    -   b) In one example, if RPR is signaled not to be used (e.g.        RPR_flag is 0) all width/height in PPS is not signaled and        inferred to be the maximum width/maximum height signaled in SPS.    -   c) In one example, if RPR is signaled not to be used (e.g.        RPR_flag is 0), conformance window information is notused in the        decoding process. Otherwise (RPR is signaled to be used),        conformance window information may be used in the decoding        process.-   31. It is proposed that the interpolation filters used in the motion    compensation process to derive the prediction block of a current    block may be selected depending on whether the resolution of the    reference picture is different to the current picture, or whether    the width and/or height of the reference picture is larger that of    the current picture.    -   a. In one example, the interpolation filters with less taps may        be applied when condition A is satisfied, wherein condition A        depends on the dimensions of the current picture and/or the        reference picture.        -   i. In one example, condition A is the resolution of the            reference picture is different to the current picture.        -   ii. In one example, condition A is the width and/or height            of the reference picture is larger than that of the current            picture.    -   iii. In one example, condition A is W1>a*W2 and/or H1>b*H2,        wherein (W1, H1) represents the width and height of the        reference picture and (W2, H2) represents the width and height        of the current picture, a and b are two factors, e.g. a=b=1.5.        -   iv. In one example, condition A may also depend on whether            bi-prediction is used.            -   1) Condition A is satisfied is satisfied only when                bi-prediction is used for the current block.        -   v. In one example, condition A may depend on M and N, where            M and N represent the width and height of the current block.            -   1) For example, condition A is satisfied only when                M*N<=T, where T is an integer such as 64.            -   2) For example, condition A is satisfied only when M<=T1                or N<=T2, where T1 and T2 are integers, e.g. T1=T2=4.            -   3) For example, condition A is satisfied only when M<=T1                and N<=T2, where T1 and T2 are integers, e.g. T1=T2=4.            -   4) For example, condition A is satisfied only when M*N                <=T, or M<=T1 or N<=T2, where T, T1 and T2 are integers,                e.g. T=64, T1=T2=4.            -   5) In one example, the smaller condition in above                sub-bullets may be replaced by greater.        -   vi. In one example, 1-tap filters are applied. In other            words, an integer pixel without filtering is output as the            interpolation result.        -   vii. In one example, bi-linear filters are applied when the            resolution of the reference picture is different to the            current picture.        -   viii. In one example, 4-tap filters or 6-tap filters are            applied when the resolution of the reference picture is            different to the current picture, or the width and/or height            of the reference picture is larger than that of the current            picture.            -   1) The 6-tap filters may also be used for the affine                motion compensation.            -   2) The 4-tap filters may also be used for interpolation                for chroma samples.    -   b. Whether to and/or how to apply the methods disclosed in        bullet 31 may depend on the color components.        -   i. For example, the methods are only applied on the luma            component.    -   c. Whether to and/or how to apply the methods disclosed in        bullet 31 may depend on the interpolation filtering direction.        -   i. For example, the methods are only applied on horizontal            filtering.        -   ii. For example, the methods are only applied on vertical            filtering.

CIIP Related

-   32. Intra prediction signal used in CIIP process may be done in TU    level instead of CU level (e.g., using reference samples outside the    TU instead of CU).    -   a) In one example, if either CU width or height is greater than        the max transform unit size, the CU may be split to multiple TUs        and intra/inter prediction may be generated for each TU, e.g.,        using reference samples outside the TU.    -   b) In one example, if the maximum transform size K is smaller        than 64 (such as K=32), then the intra-prediction used in CIIP        is performed in a recursive way like in a normal intra-code        block.    -   c) For example, a KM×KN CIIP coded block where M and N are        integers are split into MN of K×K blocks, Intra-prediction is        done for each K×K block. The intra-prediction for a later        coded/decoded K×K block may depend on the reconstruction samples        of a previously coded/decoded K×K block.

5. Additional Example Embodiments 5.1 Embodiment #1: An example ofSsyntax Design in SPS/PPS/Slice Header/Tile Group Header

The changes compared to the VTM3.0.1rc1 reference software ishighlighted in large size bold face font as follow:

 if( sps_temporal_mvp_enabled_flag )   slice_temporal_mvp_enabled_flagu(1)  if( slice_type == B )   mvd_l1_zero_flag u(1)  if(slice_temporal_mvp_enabled_flag ) {   if( slice_type == B )   collocated_from_l0_flag u(1)  } ...  if(!sps_affine_enabled_flag){   if(!(sps_sbtmvp_enabled_flag && slice_temporal_mvp_enabled_flag ))    MaxSubBlockMergeListSize = 0    else     MaxSubBlockMergeListSize =1  }  else{    five_minus_max_num_affine_merge_cand ue(v)   MaxSubBlockMergeListSize = 5− five_minus_max_num_affine_merge_cand  }

5.2 Embodiment #2: An Example of Syntax Design in SPS/PPS/SliceHeader/Tile Group Header 7.3.2.1 Sequence Parameter Set RBSP Syntax

Descriptor seq_parameter_set_rbsp( ) {  sps_seq_parameter_set_id ue(v) chroma_format_idc ue(v) ...  sps_ref_wraparound_enabled_flag u(1)  if(sps_ref_wraparound_enabled_flag )   sps_ref_wraparound_offset ue(v) sps_temporal_mvp_enabled_flag u(1)  if( sps_temporal_mvp_enabled_flag )  sps_sbtmvp_enabled_flag u(1)  sps_amvr_enabled_flag u(1) ...  } rbsp_trailing_bits( ) }

sps_sbtmvp_enabled_flag equal to 1 specifies that subblock-basedtemporal motion vector predictors may be used in decoding of pictureswith all slices having slice_type not equal to I in the CVS.sps_sbtmvp_enabled_flag equal to 0 specifies that subblock-basedtemporal motion vector predictors are not used in the CVS. Whensps_sbtmvp_enabled_flag is not present, it is inferred to be equal to 0.

five_minus_max_num_subblock_merge_cand specifies the maximum number ofsubblock-based merging motion vector prediction (MVP) candidatessupported in the slice subtracted from 5. Whenfive_minus_max_num_subblock_merge_cand is not present, it is inferred tobe equal to 5−sps_sbtmvp_enabled_flag. The maximum number ofsubblock-based merging MVP candidates, MaxNumSubblockMergeCand isderived as follows:

MaxNumSubblockMergeCand=5−five_minus_max_num_subblock_merge_cand  (7-45)

The value of MaxNumSubblockMergeCand shall be in the range of 0 to 5,inclusive.

8.3.4.2 Derivation Process for Motion Vectors and Reference Indices inSubblock Merge Mode

Inputs to this process are:

.. [No changes to the current VVC specification draft].

Outputs of this process are:

... [No changes to the current VVC specification draft].

The variables numSbX, numSbY and the subblock merging candidate list,subblockMergeCandList are derived by the following ordered steps:

When sps_sbtmvp_enabled_flag is equal to 1 and (current picture is anIRAP and index 0 of reference picture list 0 is the current picture) isnot true, the following applies:

The derivation process for merging candidates from neighbouring codingunits as specified in clause 8.3.2.3 is invoked with the luma codingblock location (xCb, yCb), the luma coding block width cbWidth, the lumacoding block height cbHeight and the luma coding block width as inputs,and the output being the availability flags availableFlagA0,availableFlagA1, availableFlagB0, availableFlagB1 and availableFlagB2,the reference indices refIdxLXA0, refIdxLXA1, refIdxLXB0, refIdxLXB1 andrefIdxLXB2, the prediction list utilization flags predFlagLXA0,predFlagLXA1, predFlagLXB0, predFlagLXB1 and predFlagLXB2, and themotion vectors mvLXA0, mvLXA1, mvLXB0, mvLXB1 and mvLXB2, with X being 0or 1.

The derivation process for subblock-based temporal merging candidates asspecified in clause 8.3.4.3 is invoked with the luma location (xCb,yCb), the luma coding block width cbWidth, the luma coding block heightcbHeight, the availability flags availableFlagA0, availableFlagA1,availableFlagB0, availableFlagB1, the reference indices refIdxLXA0,refIdxLXA1, refIdxLXB0, refIdxLXB1, the prediction list utilizationflags predFlagLXA0, predFlagLXA1, predFlagLXB0, predFlagLXB1 and themotion vectors mvLXA0, mvLXA1, mvLXB0, mvLXB1 as inputs and the outputbeing the availability flag availableFlagSbCol, the number of lumacoding subblocks in horizontal direction numSbX and in verticaldirection numSbY, the reference indices refIdxLXSbCol, the luma motionvectors mvLXSbCol[xSbIdx][ySbIdx] and the prediction list utilizationflags predFlagLXSbCol[xSbIdx][ySbIdx] with xSbIdx=0..numSbX−1, ySbIdx=0numSbY−1 and X being 0 or 1.

When sps_affine_enabled_flag is equal to 1, the sample locations (xNbA0,yNbA0), (xNbA1, yNbA1), (xNbA2, yNbA2), (xNbB0, yNbB0), (xNbB1, yNbB1),(xNbB2, yNbB2), (xNbB3, yNbB3), and the variables numSbX and numSbY arederived as follows:

[No changes to the current VVC specification draft].

5.3 Embodiment #3 An Example of MV Rounding

The syntax changes are based on JVET-O2001-vE.

8.5.5.3 Derivation Process for Subblock-Based Temporal MergingCandidates

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.        -   1. The following applies:

yColSb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1), ySb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the            following applies:

xColSb=Clip3(xCtb,Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log 2SizeY)+3), xSb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to            0), the following applies:

xColSb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log 2SizeY)+3), xSb+(tempMv[0]+8+(tempMV[0]>=0))>>4))

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

The location (xColCb, yColCb) of the collocated block inside ColPic isderived as follows.

-   -   The following applies:

yColCb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1), yColCtrCb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb,Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3),xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0,        the following applies:

xColCb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

5.3 Embodiment #3: An Example of MV Rounding

The syntax changes are based on JVET-O2001-vE.

8.5.5.3 Derivation Process for Subblock-Based Temporal MergingCandidates

-   The location (xColSb, yColSb) of the collocated subblock inside    ColPic is derived as follows.    -   1. The following applies:

yColSb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1),ySb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColSb=Clip3(xCtb,Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3), xSb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xColSb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xSb+(tempMv[0]+8+(tempMV[0]>=0))>>4))

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

The location (xColCb, yColCb) of the collocated block inside ColPic isderived as follows.

-   -   The following applies:

yColCb=Clip3(yCtb,Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1),yColCtrCb+((tempMv[1]+8−(tempMv[1]>=0))>>4))

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb,Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3),xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0,        the following applies:

xColCb=Clip3(xCtb,Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xColCtrCb+((tempMv[0]+8+(tempMV[0]>=0))>>4))

5.4 Embodiment #4: A Second Example of MV Rounding 8.5.5.3 DerivationProcess for Subblock-Based Temporal Merging Candidates

Inputs to this process are:

-   a luma location (xCb, yCb) of the top-left sample of the current    luma coding block relative to the top-left luma sample of the    current picture,-   a variable cbWidth specifying the width of the current coding block    in luma samples,-   a variable cbHeight specifying the height of the current coding    block in luma samples.-   the availability flag availableFlagA₁ of the neighbouring coding    unit,-   the reference index refIdxLXA₁ of the neighbouring coding unit with    X being 0 or 1,-   the prediction list utilization flag predFlagLXA₁ of the    neighbouring coding unit with X being 0 or 1,-   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of the    neighbouring coding unit with X being 0 or 1.

Outputs of this process are:

-   the availability flag availableFlagSbCol,-   the number of luma coding subblocks in horizontal direction numSbX    and in vertical direction numSbY,-   the reference indices refIdxL0SbCol and refIdxL1SbCol,-   the luma motion vectors in 1/16 fractional-sample accuracy    mvLOSbCol[xSbIdx][ySbIdx] and mvL1SbCol[xSbIdx][ySbIdx] with    xSbIdx=0..numSbX−1, ySbIdx=0..numSbY−1,-   the prediction list utilization flags    predFlagLOSbCol[xSbIdx][ySbIdx] and predFlagL1SbCol[xSbIdx][ySbIdx]    with xSbIdx=0..numSbX−1, ySbIdx=0 numSbY−1.

The availability flag availableFlagSbCol is derived as follows.

-   If one or more of the following conditions is true, availableFlagSb    Col is set equal to 0.-   slice temporal mvp enabled flag is equal to 0.-   sps sbtmvp enabled flag is equal to 0.-   cbWidth is less than 8.-   cbHeight is less than 8.-   Otherwise, the following ordered steps apply:    -   1. The location (xCtb, yCtb) of the top-left sample of the luma        coding tree block that contains the current coding block and the        location (xCtr, yCtr) of the below-right center sample of the        current luma coding block are derived as follows:

xCtb=(xCb>>Ctu Log 2Size)<<Ctu Log2Size   (8-542)

yCtb=(yCb>>Ctu Log 2Size)<<Ctu Log2Size   (8-543)

xCtr=xCb+(cbWidth/2)   (8-544)

yCtr=yCb+(cbHeight/2)   (8-545)

-   -   2. The luma location (xColCtrCb, yColCtrCb) is set equal to the        top-left sample of the collocated luma coding block covering the        location given by (xCtr, yCtr) inside ColPic relative to the        top-left luma sample of the collocated picture specified by        ColPic.    -   3. The derivation process for subblock-based temporal merging        base motion data as specified in clause 8.5.5.4 is invoked with        the location (xCtb, yCtb), the location (xColCtrCb, yColCtrCb),        the availability flag availableFlagA₁, and the prediction list        utilization flag predFlagLXA₁, and the reference index        refIdxLXA₁, and the motion vector mvLXA₁, with X being 0 and 1        as inputs and the motion vectors ctrMvLX, and the prediction        list utilization flags ctrPredFlagLX of the collocated block,        with X being 0 and 1, and the temporal motion vector tempMv as        outputs.    -   4. The variable availableFlagSbCol is derived as follows:        -   If both ctrPredFlagL0 and ctrPredFlagL1 are equal to 0,            availableFlagSbCol is set equal to 0.        -   Otherwise, availableFlagSbCol is set equal to 1.

When availableFlagSbCol is equal to 1, the following applies:

-   The variables numSbX, numSbY, sbWidth, sbHeight and refIdxLXSbCol    are derived as follows:

numSbX=cbWidth>>3   (8-546)

numSbY=cbHeight>>3   (8-547)

sbWidth=cbWidth/numSbX   (8-548)

sbHeight=cbHeight/numSbY   (8-549)

refIdxLXSbCol=0   (8-550)

-   For xSbIdx=0..numSbX−1 and ySbIdx=0..numSbY−1, the motion vectors    mvLXSbCol[xSbIdx][ySbIdx] and prediction list utilization flags    predFlagLXSbCol[xSbIdx][ySbIdx] are derived as follows:    -   The luma location (xSb, ySb) specifying the top-left sample of        the current coding subblock relative to the top-left luma sample        of the current picture is derived as follows:

xSb=xCb+xSbIdx*sbWidth+sbWidth/2   (8-551)

ySb=yCb+ySbIdx*sbHeight+sbHeight/2   (8-552)

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.        -   1. The following applies:

yColSb=Clip3(yCtb, Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1), ySb+((tempMv[1]+8−(tempMv[1]>=0 ? 1:0))>>4))    (8-553)

-   -   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the            following applies:

xColSb=Clip3(xCtb, Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3), xSb+((tempMv[0]+8−(tempMv[0]>=0 ? 1:0))>>4))    (8-554)

-   -   -   Otherwise (subpic treated as pic flag[SubPicIdx] is equal to            0), the following applies:

xColSb=Clip3(xCtb, Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xSb+((tempMv[0]+8−(tempMv[0]>=0 ? 1:0))>>4))   (8-555)

-   -   The variable currCb specifies the luma coding block covering the        current coding subblock inside the current picture.    -   The variable colCb specifies the luma coding block covering the        modified location given by ((xColSb>>3)<<3, (yColSb>>3)<<3)        inside the ColPic.    -   The luma location (xColCb, yColCb) is set equal to the top-left        sample of the collocated luma coding block specified by colCb        relative to the top-left luma sample of the collocated picture        specified by ColPic.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL0 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL0SbCol[xSbIdx][ySbIdx] and        availableFlagLOSbCol.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL1 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL1SbCol[xSbIdx][ySbIdx] and        availableFlagL1SbCol.    -   When availableFlagL0SbCol and availableFlagL1SbCol are both        equal to 0, the following applies for X being 0 and 1:

mvLXSbCol[xSbIdx][ySbIdx]=ctrMvLX   (8-556)

predFlagLXSbCol[xSbIdx][ySbIdx]=ctrPredFlagLX   (8-557)

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

Inputs to this process are:

-   the location (xCtb, yCtb) of the top-left sample of the luma coding    tree block that contains the current coding block,-   the location (xColCtrCb, yColCtrCb) of the top-left sample of the    collocated luma coding block that covers the below-right center    sample.-   the availability flag availableFlagA₁ of the neighbouring coding    unit,-   the reference index refIdxLXA₁ of the neighbouring coding unit,-   the prediction list utilization flag predFlagLXA_(i) of the    neighbouring coding unit,-   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of the    neighbouring coding unit.

Outputs of this process are:

-   the motion vectors ctrMvL0 and ctrMvL1,-   the prediction list utilization flags ctrPredFlagL0 and    ctrPredFlagL1,-   the temporal motion vector tempMv.

The variable tempMv is set as follows:

tempMv[0]=0   (8-558)

tempMv[1]=0   (8-559)

The variable currPic specifies the current picture.

When availableFlagA_(i) is equal to TRUE, the following applies:

-   If all of the following conditions are true, tempMv is set equal to    mvL0A₁:    -   predFlagL0A₁ is equal to 1,    -   DiffPicOrderCnt(ColPic, RefPicList[0][refIdxL0A₁]) is equal to        0,-   Otherwise, if all of the following conditions are true, tempMv is    set equal to mvL1A₁:    -   slice_type is equal to B,    -   predFlagL1A₁ is equal to 1,    -   DiffPicOrderCnt(ColPic, RefPicList[1][refIdxL1A₁]) is equal to        0.

The location (xColCb, yColCb) of the collocated block inside ColPic isderived as follows.

-   -   The following applies:

yColCb=Clip3(yCtb, Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY) −1), yColCtrCb+((tempMv[1]+8−(tempMv[1]>=0 ? 1:0))>>4))  (8-560)

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb, Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3), xColCtrCb+((tempMv[0]+8−(tempMv[0]>=0 ? 1:0))>>4))   (8-561)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to o,        the following applies:

xColCb=Clip3(xCtb, Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xColCtrCb+((tempMv[0]+8−(tempMv[0]>=0 ? 1:0))>>4))   (8-562)

The array colPredMode is set equal to the prediction mode arrayCuPredMode[0] of the collocated picture specified by ColPic.

The motion vectors ctrMvL0 and ctrMvL1, and the prediction listutilization flags ctrPredFlagL0 and ctrPredFlagL1 are derived asfollows:

-   -   If colPredMode[xColCb][yColCb] is equal to MODE INTER, the        following applies:        -   The variable currCb specifies the luma coding block covering            (xCtrCb,yCtrCb) inside the current picture.        -   The variable colCb specifies the luma coding block covering            the modified location given by ((xColCb>>3)<<3,            (yColCb>>3)<<3) inside the ColPic.        -   The luma location (xColCb, yColCb) is set equal to the            top-left sample of the collocated luma coding block            specified by colCb relative to the top-left luma sample of            the collocated picture specified by ColPic.        -   The derivation process for collocated motion vectors            specified in clause 8.5.2.12 is invoked with currCb, colCb,            (xColCb, yColCb), refIdxL0 set equal to 0, and sbFlag set            equal to 1 as inputs and the output being assigned to            ctrMvL0 and ctrPredFlagL0.        -   The derivation process for collocated motion vectors            specified in clause 8.5.2.12 is invoked with currCb, colCb,            (xColCb, yColCb), refIdxL1 set equal to 0, and sbFlag set            equal to 1 as inputs and the output being assigned to            ctrMvL1 and ctrPredFlagL1.    -   Otherwise, the following applies:

ctrPredFlagL0=0   (8-563)

ctrPredFlagL1=0   (8-564)

5.5 Embodiment #5: A Third Example of MV Rounding 8.5.5.3 DerivationProcess for Subblock-Based Temporal Merging Candidates

Inputs to this process are:

-   a luma location (xCb, yCb) of the top-left sample of the current    luma coding block relative to the top-left luma sample of the    current picture,-   a variable cbWidth specifying the width of the current coding block    in luma samples,-   a variable cbHeight specifying the height of the current coding    block in luma samples.-   the availability flag availableFlagA₁ of the neighbouring coding    unit,-   the reference index refIdxLXA₁ of the neighbouring coding unit with    X being 0 or 1,-   the prediction list utilization flag predFlagLXA₁ of the    neighbouring coding unit with X being 0 or 1,-   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of the    neighbouring coding unit with X being 0 or 1.

Outputs of this process are:

-   the availability flag availableFlagSbCol,-   the number of luma coding subblocks in horizontal direction numSbX    and in vertical direction num SbY,-   the reference indices refIdxL0SbCol and refIdxL1SbCol,-   the luma motion vectors in 1/16 fractional-sample accuracy    mvL0SbCol[xSbIdx][ySbIdx] and myL1SbCol[xSbIdx][ySbIdx] with    xSbIdx=0..numSbX−1, ySbIdx=0..num SbY−1,-   the prediction list utilization flags    predFlagL0SbCol[xSbIdx][ySbIdx] and predFlagL1SbCol[xSbIdx][ySbIdx]    with xSbIdx=0..numSbX−1, ySbIdx=0..numSbY−1.

The availability flag availableFlagSbCol is derived as follows.

-   If one or more of the following conditions is true,    availableFlagSbCol is set equal to 0.-   slice temporal mvp enabled flag is equal to 0.-   sps sbtmvp enabled flag is equal to 0.-   cbWidth is less than 8.-   cbHeight is less than 8.-   Otherwise, the following ordered steps apply:    -   1. The location (xCtb, yCtb) of the top-left sample of the luma        coding tree block that contains the current coding block and the        location (xCtr, yCtr) of the below-right center sample of the        current luma coding block are derived as follows:

xCtb=(xCb>>Ctu Log 2 Size)<<Ctu Log2 Size   (8-542)

yCtb=(yCb>>Ctu Log 2Size)<<Ctu Log2 Size   (8-543)

xCtr=xCb+(cbWidth/2)   (8-544)

yCtr=yCb+(cbHeight/2)   (8-545)

-   -   2. The luma location (xColCtrCb, yColCtrCb) is set equal to the        top-left sample of the collocated luma coding block covering the        location given by (xCtr, yCtr) inside ColPic relative to the        top-left luma sample of the collocated picture specified by        ColPic.    -   3. The derivation process for subblock-based temporal merging        base motion data as specified in clause 8.5.5.4 is invoked with        the location (xCtb, yCtb), the location (xColCtrCb, yColCtrCb),        the availability flag availableFlagA₁, and the prediction list        utilization flag predFlagLXA₁, and the reference index        refIdxLXA₁, and the motion vector mvLXA₁, with X being 0 and 1        as inputs and the motion vectors ctrMvLX, and the prediction        list utilization flags ctrPredFlagLX of the collocated block,        with X being 0 and 1, and the temporal motion vector tempMv as        outputs.    -   4. The variable availableFlagSbCol is derived as follows:        -   If both ctrPredFlagL0 and ctrPredFlagL1 are equal to 0,            availableFlagSbCol is set equal to 0.        -   Otherwise, availableFlagSbCol is set equal to 1.

When availableFlagSbCol is equal to 1, the following applies:

-   -   The variables numSbX, numSbY, sbWidth, sbHeight and        refIdxLXSbCol are derived as follows:

numSbX=cbWidth>>3   (8-546)

numSbY=cbHeight>>3   (8-547)

sbWidth=cbWidth/numSbX   (8-548)

sbHeight=cbHeight/numSbY   (8-549)

refIdxLXSbCol=0   (8-550)

-   -   For xSbIdx=0..numSbX−1 and ySbIdx=0..numSbY−1, the motion        vectors mvLXSbCol[xSbIdx][ySbIdx] and prediction list        utilization flags predFlagT XSbCol[xSbIdx][ySbIdx] are derived        as follows:        -   The luma location (xSb, ySb) specifying the top-left sample            of the current coding subblock relative to the top-left luma            sample of the current picture is derived as follows:

xSb=xCb+xSbIdx*sbWidth+sbWidth/2   (8-551)

ySb=yCb+ySbIdx*sbHeight+sbHeight/2   (8-552)

-   -   The location (xColSb, yColSb) of the collocated subblock inside        ColPic is derived as follows.    -   1. The following applies:

yColSb=Clip3(yCtb, Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1), ySb+((tempMv[1]+(tempMv[1]>=0 ? 7:8))>>4))   (8-553)

-   -   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the        following applies:

xColSb=Clip3(xCtb, Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3), xSb+((tempMv[0]+(tempMv[0]>=0 ? 7:8))>>4))   (8-554)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0),        the following applies:

xColSb=Clip3(xCtb, Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xSb+((tempMv[0]+(tempMv[0]>=0 ? 7:8))>>4))   (8-555)

-   -   The variable currCb specifies the luma coding block covering the        current coding subblock inside the current picture.    -   The variable colCb specifies the luma coding block covering the        modified location given by ((xColSb>>3)<<3, (yColSb>>3)<<3)        inside the ColPic.    -   The luma location (xColCb, yColCb) is set equal to the top-left        sample of the collocated luma coding block specified by colCb        relative to the top-left luma sample of the collocated picture        specified by ColPic.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL0 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL0 Sb Col[xSbIdx][ySbIdx] and        availableFlagL0SbCol.    -   The derivation process for collocated motion vectors as        specified in clause 8.5.2.12 is invoked with currCb, colCb,        (xColCb, yColCb), refIdxL1 set equal to 0 and sbFlag set equal        to 1 as inputs and the output being assigned to the motion        vector of the subblock mvL1SbCol[xSbIdx][ySbIdx] and        availableFlagL1SbCol.    -   When availableFlagLOSbCol and availableFlagL1 SbCol are both        equal to 0, the following applies for X being 0 and 1:

mvLXSbCol[xSbIdx][ySbIdx]=ctrMvLX   (8-556)

predFlagLXSbCol[xSbIdx][ySbIdx]=ctrPredFlagLX   (8-557)

8.5.5.4 Derivation Process for Subblock-Based Temporal Merging BaseMotion Data

Inputs to this process are:

-   the location (xCtb, yCtb) of the top-left sample of the luma coding    tree block that contains the current coding block,-   the location (xColCtrCb, yColCtrCb) of the top-left sample of the    collocated luma coding block that covers the below-right center    sample.-   the availability flag availableFlagA₁ of the neighbouring coding    unit,-   the reference index refIdxLXA₁ of the neighbouring coding unit,-   the prediction list utilization flag predFlagLXA₁ of the    neighbouring coding unit,-   the motion vector in 1/16 fractional-sample accuracy mvLXA₁ of the    neighbouring coding unit.

Outputs of this process are:

-   the motion vectors ctrMvL0 and ctrMvL1,-   the prediction list utilization flags ctrPredFlagL0 and    ctrPredFlagL1,-   the temporal motion vector tempMv.

The variable tempMv is set as follows:

tempMv[0]=0   (8-558)

tempMv[1]=0   (8-559)

The variable currPic specifies the current picture.

When availableFlagA₁ is equal to TRUE, the following applies:

-   If all of the following conditions are true, tempMv is set equal to    mvL0A₁:    -   predFlagL0A₁ is equal to 1,    -   DiffPicOrderCnt(ColPic, RefPicList[0][refIdxL0A₁]) is equal to        0,-   Otherwise, if all of the following conditions are true, tempMv is    set equal to mvLlA₁:    -   slice type is equal to B,    -   predFlagL1A₁ is equal to 1,    -   DiffPicOrderCnt(ColPic, RefPicList[1][refIdxL1A₁]) is equal to        0.

The location (xColCb, yColCb) of the collocated block inside ColPic isderived as follows.

-   -   The following applies:

yColCb=Clip3(yCtb, Min(CurPicHeightInSamplesY−1, yCtb+(1<<Ctb Log2SizeY)−1), yColCtrCb+((tempMv[1]+(tempMv[1]>=0 ? 7:8))>>4))   (8-560)

-   -   If subpic treated as pic flag[SubPicIdx] is equal to 1, the        following applies:

xColCb=Clip3(xCtb, Min(SubPicRightBoundaryPos, xCtb+(1<<Ctb Log2SizeY)+3), xColCtrCb+((tempMv[0]+(tempMv[0]>=0 ? 7:8))>>4))   (8-561)

-   -   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to o,        the following applies:

xColCb=Clip3(xCtb, Min(CurPicWidthInSamplesY−1, xCtb+(1<<Ctb Log2SizeY)+3), xColCtrCb+((tempMv[0]+(tempMv[0]>=0 ? 7:8))>>4))   (8-562)

The array colPredMode is set equal to the prediction mode arrayCuPredMode[0] of the collocated picture specified by ColPic.

The motion vectors ctrMvL0 and ctrMvLl, and the prediction listutilization flags ctrPredFlagL0 and ctrPredFlagL1 are derived asfollows:

-   If colPredMode[xColCb][yColCb] is equal to MODE INTER, the following    applies:    -   The variable currCb specifies the luma coding block covering        (xCtrCb ,yCtrCb) inside the current picture.    -   The variable colCb specifies the luma coding block covering the        modified location given by ((xColCb>>3)<<3, (yColCb>>3)<<3)        inside the ColPic.    -   The luma location (xColCb, yColCb) is set equal to the top-left        sample of the collocated luma coding block specified by colCb        relative to the top-left luma sample of the collocated picture        specified by ColPic.    -   The derivation process for collocated motion vectors specified        in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb,        yColCb), refIdxL0 set equal to 0, and sbFlag set equal to 1 as        inputs and the output being assigned to ctrMvL0 and        ctrPredFlagL0.    -   The derivation process for collocated motion vectors specified        in clause 8.5.2.12 is invoked with currCb, colCb, (xColCb,        yColCb), refIdxL1 set equal to 0, and sbFlag set equal to 1 as        inputs and the output being assigned to ctrMvL1 and ctrPredFlagT        1.-   Otherwise, the following applies:

ctrPredFlagL0=0   (8-563)

ctrPredFlagL1=0   (8-564)

8.5.6.3 Fractional Sample Interpolation Process 8.5.6.3.1 General

Inputs to this process are:

-   a luma location (xSb, ySb) specifying the top-left sample of the    current coding subblock relative to the top-left luma sample of the    current picture,-   a variable sbWidth specifying the width of the current coding    subblock,-   a variable sbHeight specifying the height of the current coding    subblock,-   a motion vector offset mvOffset,-   a refined motion vector refMvLX,-   the selected reference picture sample array refPicLX,-   the half sample interpolation filter index hpelIfIdx,-   the bi-directional optical flow flag bdofFlag,-   a variable cIdx specifying the colour component index of the current    block.

Outputs of this process are:

-   an (sbWidth+brdExtSize)×(sbHeight+brdExtSize) array predSamplesLX of    prediction sample values.

The prediction block border extension size brdExtSize is derived asfollows:

brdExtSize=(bdofFlag∥(inter_affine_flag[xSb][ySb] &&sps_affine_prof_enabled_flag)) ? 2:0    (8-752)

The variable fRefWidth is set equal to the PicOutputWidthL of thereference picture in luma samples.

The variable fRefHeight is set equal to PicOutputHeightL of thereference picture in luma samples.

The motion vector mvLX is set equal to (refMvLX−mvOffset).

-   If cIdx is equal to 0, the following applies:    -   The scaling factors and their fixed-point representations are        defined as

hori_scale_fp=((fRefWidth<<14)+(PicOutputWidthL>>1))/PicOutputWidthL  (8-753)

vert_scale_fp=((fRefHeight<<14)+(PicOutputHeightL>>1))/PicOutputHeightL  (8-754)

-   -   Let (xIntL, yIntL) be a luma location given in full-sample units        and (xFracL, yFracL) be an offset given in 1/16-sample units.        These variables are used only in this clause for specifying        fractional-sample locations inside the reference sample arrays        refPicLX.    -   The top-left coordinate of the bounding block for reference        sample padding (xSbInt_(L), ySbInt_(L)) is set equal to        (xSb+(mvLX[0]>>4), ySb+(mvLX[1]>>4)).    -   For each luma sample location (x_(L)=0..sbWidth−1+brdExtSize,        y_(L)=0..sbHeight−1+brdExtSize) inside the prediction luma        sample array predSamplesLX, the corresponding prediction luma        sample value predSamplesLX[x_(L)][y_(L)] is derived as follows:        -   Let (refxSb_(L), refySb_(L)) and (refx_(L), refy_(L)) be            luma locations pointed to by a motion vector (refMvLX[0],            refMvLX[1])given in 1/16-sample units. The variables            refxSb_(L), refx_(L), refySb_(L), and refy_(L) are derived            as follows:

refxSb _(L)=((xSb<<4)+refMvLX[0])*hori_scale_fp   (8-755)

refx _(L)=((Sign(refxSb)*((Abs(refxSb)+128)>>8)+x_(L)*((hori_scale_fp+8)>>4))+32)>>6   (8-756)

refySb_(L)=((ySb<<4)+refMvLX[1])*vert_scale_fp   (8-757)

refyL=((Sign(refySb)*((Abs(refySb)+128)>>8)+yL*((vert_scale_fp+8)>>4))+32)>>6  (8-758)

-   -   The variables xInt_(L), yInt_(L), xFrac_(L) and yFrac_(L) are        derived as follows:

xInt_(L)=refx_(L)>>4   (8-759)

yInt_(L)=refy_(L)>>4   (8-760)

xFrac_(L)=refx_(L) & 15   (8-761)

yFrac_(L)=refy_(L) & 15   (8-762)

-   using6TapFlag is set to be 1 if all the conditions below are    satisfied:

cbWidth[0][xSb][ySb]<=4∥cbHeight[0][xSb][ySb]<=4∥cbWidth[0][xSb][ySb]*cbHeight[0][xSb][ySb]<=64.

PredFlagL0[xSb][ySb]==1 && PredFlagL1[xSb][ySb]1.

-   If bdofFlag is equal to TRUE or (sps_affine_prof_enabled_flag is    equal to TRUE and inter_affine_flag[xSb][ySb] is equal to TRUE), and    one or more of the following conditions are true, the prediction    luma sample value predSamplesLX[x_(L)][y_(L)] is derived by invoking    the luma integer sample fetching process as specified in clause    8.5.6.3.3 with (xInt_(L)+(xFrac_(L)>>3)−1),    yInt_(L)+(yFrac_(L)>>3)−1) and refPicLX as inputs.    -   1. x_(L) is equal to 0.    -   2. x_(L) is equal to sbWidth+1.    -   3. y_(L) is equal to 0.    -   4. y_(L) is equal to sbHeight+1.-   Otherwise, the prediction luma sample value predSamplesLX[xL][yL] is    derived by invoking the luma sample 8-tap interpolation filtering    process as specified in clause 8.5.6.3.2 with (xIntL−(brdExtSize>0 ?    1:0), yIntL−(brdExtSize>0 ? 1:0)), (xFracL, yFracL), (xSbInt_(L),    ySbInt_(L)), refPicLX, hpelIfIdx, sbWidth, sbHeight and (xSb, ySb)    and using6TapFlag as inputs.-   Otherwise (cIdx is not equal to 0), the following applies:    -   Let (xIntC, yIntC) be a chroma location given in full-sample        units and (xFracC, yFracC) be an offset given in 1/32 sample        units. These variables are used only in this clause for        specifying general fractional-sample locations inside the        reference sample arrays refPicLX.    -   The top-left coordinate of the bounding block for reference        sample padding (xSbIntC, ySbIntC) is set equal to        ((xSb/SubWidthC)+(mvLX[0]>>5), (ySb/SubHeightC)+(mvLX[1]>>5)).    -   For each chroma sample location (xC=0..sbWidth−1,        yC=0..sbHeight−1) inside the prediction chroma sample arrays        predSamplesLX, the corresponding prediction chroma sample value        predSamplesLX[xC][yC] is derived as follows:        -   Let (refxSb_(C), refy Sb_(C)) and (refx_(C), refy_(C)) be            chroma locations pointed to by a motion vector (mvLX[0],            mvLX[1]) given in 1/32-sample units. The variables            refxSb_(C), refySb_(C), refx_(C) and refy_(C) are derived as            follows:

refxSb _(C)=((xSb/SubWidthC<<5)+mvLX[0])*hori_scale_fp   (8-763)

refx _(C)=((Sign(refxSb _(C))*((Abs(refxSb_(C))+256)>>9)+xC*((hori_scale_fp+8)>>4))+16)>>5   (8-764)

refySb _(C)=((ySb/SubHeightC<<5)+mvLX[1])*vert_scale_fp   (8-765)

refy _(C)=((Sign(refySb _(C))*((Abs(refySb_(C))+256)>>9)+yC*((vert_scale_fp+8)>>4))+16)>>5   (8-766)

-   -   -   The variables xInt_(C), yInt_(C), xFrac_(C) and yFrac_(C)            are derived as follows:

xInt_(C)=refx_(C)>>5   (8-767)

yInt_(C)=refy_(C)>>5   (8-768)

xFrac_(C)=refy_(C) & 31   (8-769)

yFrac_(C)=refy_(C) & 31   (8-770)

-   -   The prediction sample value predSamplesLX[xC][yC] is derived by        invoking the process specified in clause 8.5.6.3.4 with (xIntC,        yIntC), (xFracC, yFracC), (xSbIntC, ySbIntC), sbWidth, sbHeight        and refPicLX as inputs.

8.5.6.3.2 Luma Sample Interpolation Filtering Process

Inputs to this process are:

-   a luma location in full-sample units (xInt_(L), yInt_(L)),-   a luma location in fractional-sample units (xFrac_(L), yFrac_(L)),-   a luma location in full-sample units (xSbInt_(L), ySbInt_(L))    specifying the top-left sample of the bounding block for reference    sample padding relative to the top-left luma sample of the reference    picture,-   the luma reference sample array refPicLX_(L),-   the half sample interpolation filter index hpelIfIdx,-   a variable sbWidth specifying the width of the current subblock,-   a variable sbHeight specifying the height of the current subblock,-   a luma location (xSb, ySb) specifying the top-left sample of the    current subblock relative to the top-left luma sample of the current    picture,-   a flag using6TapFlag specifying whether the 6-tap interpolation    filter used.

Output of this process is a predicted luma sample value predSampleLX_(L)

The variables shift1, shift2 and shift3 are derived as follows:

-   The variable shiftl is set equal to Min(4, BitDepth_(Y)−8), the    variable shift2 is set equal to 6 and the variable shift3 is set    equal to Max(2, 14−BitDepth_(Y)).-   The variable picW is set equal to pic_width_in_luma_samples and the    variable picH is set equal to pic_height_in_luma_samples.

The luma interpolation filter coefficients f_(L)[p] for each 1/16fractional sample position p equal to xFrac_(L) or yFrac_(L) are derivedas follows:

0 If at least one of the following conditions are satisfied, the lumainterpolation filter coefficients f_(L)[p] are specified in Table 8-12.

-   -   MotionModelIdc[xSb][ySb] is greater than 0, and sbWidth and        sbHeight are both equal to 4,    -   using6TapFlag is equal to 1.

-   Otherwise, the luma interpolation filter coefficients f_(L)[p] are    specified in Table 8-11 depending on hpellfIdx.

The luma locations in full-sample units (xInt_(i), yInt_(i)) are derivedas follows for i=0..7:

-   If subpic_treated_as_pic_flag[SubPicIdx] is equal to 1, the    following applies:

xInt_(i)=Clip3(SubPicLeftBoundaryPos, SubPicRightBoundaryPos, xInt_(L)+i−3)   (8-771)

yInt_(i)=Clip3(SubPicTopBoundaryPos, SubPicBotBoundaryPos, yInt_(L)+i−3)   (8-772)

-   Otherwise (subpic_treated_as_pic_flag[SubPicIdx] is equal to 0), the    following applies:

xInt_(i)=Clip3(0, picW−1, sps_ref_wraparound_enabled_flag ?ClipH((sps_ref_wraparound_offset_minus1+1)*MinCbSizeY, picW, xInt_(L)+i−3): xInt_(L) +i−3)   (8-773)

yint_(i)=Clip3(0, picH−1, yInt_(L) +i−3)    (8-774)

The luma locations in full-sample units are further modified as followsfor i=0..7:

xInt_(i)=Clip3(xSbInt_(L)−3, xSbInt_(L) +sbWidth+4, xInt_(i))   (8-775)

yInt_(i)=Clip3(ySbInt_(L)−3, ySbInt_(L) +sbHeight+4, yInt_(i))   (8-776)

The predicted luma sample value predSampleLX_(L) is derived as follows:

-   If both xFrac_(L) and yFrac_(L) are equal to 0, the value of    predSampleLX_(L) is derived as follows:

predSampleLX _(L)=refPicLX _(L) [xInt₃ ][yInt₃]<<shift3   (8-777)

-   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is equal to    0, the value of predSampleLX_(L) is derived as follows:

predSampleLX _(L)=(Σ_(i=0) ⁷ f _(L) [xFrac_(L) ][i]*refPicLX _(L)[xInt_(i) ][yInt₃])>>shift1    (8-778)

-   Otherwise, if xFrac_(L) is equal to 0 and yFrac_(L) is not equal to    0, the value of predSampleLX_(L) is derived as follows:

predSampleLX _(L)=(Σ_(i=) ⁷ [yFrac_(L) ][i]*refPicLX _(L) [xInt₃][yInt])>>shift1    (8-779)

-   Otherwise, if xFrac_(L) is not equal to 0 and yFrac_(L) is not equal    to 0, the value of predSampleLX_(L) is derived as follows:    -   The sample array temp[n] with n=0..7, is derived as follows:

temp[n]=(Σ_(i=0) ⁷ f _(L) [xFrac_(L) ][i]*refPicLX _(L) [xInt_(i)][yInt_(n)])>>shift1   (8-780)

-   -   The predicted luma sample value predSampleLX_(L) is derived as        follows:

predSampleLX _(L)=(Σ_(i=0) ⁷ f _(L) [yFrac_(L) ][i]*temp[i])>>shift2  (8-781)

TABLE 8-11 Specification of the luma interpolation filter coefficientsf_(L)[p] for each 1/16 fractional sample position p. Fractional sampleinterpolation filter coefficients position f_(L)[p][0] f_(L)[p][1]f_(L)[p][2] f_(L)[p][3] f_(L)[p][4] f_(L)[p][5] f_(L)[p][6] f_(L)[p][7]1 0 1 −3 63 4 −2 1 0 2 −1 2 −5 62 8 −3 1 0 3 −1 3 −8 60 13 −4 1 0 4 −1 4−10 58 17 −5 1 0 5 −1 4 −11 52 26 −8 3 −1 6 −1 3 −9 47 31 −10 4 −1 7 −14 −11 45 34 −10 4 −1 8 −1 4 −11 40 40 −11 4 −1 (hpelIfIdx == 0) 8 0 3 920 20 9 3 0 (hpelIfIdx == 1) 9 −1 4 −10 34 45 −11 4 −1 10 −1 4 −10 31 47−9 3 −1 11 −1 3 −8 26 52 −11 4 −1 12 0 1 −5 17 58 −10 4 −1 13 0 1 −4 1360 −8 3 −1 14 0 1 −3 8 62 −5 2 −1 15 0 1 −2 4 63 −3 1 0

TABLE 8-12 Specification of the luma interpolation filter coefficientsf_(L)[p] for each 1/16 fractional sample position p for affine motionmode. Fractional sample position interpolation filter coefficients pf_(L)[p][0] f_(L)[p][1] f_(L)[p][2] f_(L)[p][3] f_(L)[p][4] f_(L)[p][5]f_(L)[p][6] f_(L)[p][7] 1 0 1 −3 63 4 −2 1 0 2 0 1 −5 62 8 −3 1 0 3 0 2−8 60 13 −4 1 0 4 0 3 −10 58 17 −5 1 0 5 0 3 −11 52 26 −8 2 0 6 0 2 −947 31 −10 3 0 7 0 3 −11 45 34 −10 3 0 8 0 3 −11 40 40 −11 3 0 9 0 3 −1034 45 −11 3 0 10 0 3 −10 31 47 −9 2 0 11 0 2 −8 26 52 −11 3 0 12 0 1 −517 58 −10 3 0 13 0 1 −4 13 60 −8 2 0 14 0 1 −3 8 62 −5 1 0 15 0 1 −2 463 −3 1 0

FIG. 29 is a block diagram of a video processing apparatus 2600. Theapparatus 2600 may be used to implement one or more of the methodsdescribed herein. The apparatus 2600 may be embodied in a smartphone,tablet, computer, Internet of Things (IoT) receiver, and so on. Theapparatus 2600 may include one or more processors 2602, one or morememories 2604 and video processing hardware 2606. The processor(s) 2602may be configured to implement one or more methods described in thepresent document. The memory (memories) 2604 may be used for storingdata and code used for implementing the methods and techniques describedherein. The video processing hardware 2606 may be used to implement, inhardware circuitry, some techniques described in the present document.

FIG. 30 is a flowchart for an example method 3000 of video processing.The method includes determining (3002), for a current video block, amaximum number of candidates ML in a sub-block merge candidate list orenabling a use of alternative temporal motion vector prediction (ATMVP)candidates based on a state of use of temporal motion vector prediction(TMVP) or current picture referencing coding (CPR) for the current videoblock, wherein the state is one of enabled or disabled and performing(3004), based on a result of the determining, a conversion between thecurrent video block and a bitstream representation of the current videoblock.

It will be appreciated that several techniques have been disclosed thatwill benefit video encoder and decoder embodiments incorporated withinvideo processing devices such as smartphones, laptops, desktops, andsimilar devices by allowing the use of ATMVP coding tool in encoding ordecoding of video or images. Various embodiments and techniques may bedescribed using the following clause-based description.

1. A method of video processing, comprising: determining, for a currentvideo block, a maximum number of candidates ML in a sub-block mergecandidate list or enabling a use of alternative temporal motion vectorprediction (ATMVP) candidates based on a state of use of temporal motionvector prediction (TMVP) or a state of current picture referencingcoding (CPR) for the current video block, wherein the state is one ofenabled or disabled, and performing, based on a result of thedetermining, a conversion between the current video block and abitstream representation of the current video block.

2. The method of clause 1, wherein the enabling the use of ATMVPcandidates is further based on a state of ATMVP usage for the currentvideo block.

3. The method of any of claims 1-2, wherein the determining ML includes:determining that ATMVP and TMVP are disabled; and determining ML byexcluding ATMVP candidates from the sub-block merge candidate list.

4. The method of any of claims 1-2, wherein the determining ML includes:

-   -   concluding that ATMVP is enabled for the current video block,        TMVP is disabled for the current video block and affine coding        is disabled for the current video block; and    -   based on the concluding, setting ML to zero.

5 The method of any of claims 1-2, wherein the determining ML includes:

-   -   concluding that ATMVP is enabled for the current video block,        TMVP is enabled for the current video block and affine coding is        disabled for the current video block; and    -   based on the concluding, setting ML to 1.

6. The method of any of claims 1-2, wherein the determining ML is basedon the state of ATMVP usage for the current block, and whether acollocated reference picture of a current picture of the current videoblock is the current picture.

7. The method of any of claims 1-2, wherein the determining ML is basedon the state of ATMVP, and whether a reference picturewith referenceindex 0 in a reference picture list of a current picture of the currentvideo block is the current picture.

8. The method of clause 7, wherein the reference picture list is eitherlist 0 or list 1.

Additional description of clauses 1-8 can be found in the items 1-2listed in Section 4.

9. A method of video processing, comprising:

-   -   determining, fora conversion between a bitstream representing a        sequence of video pictures and pixel values of the video picture        using a block-based encoding in which blocks of a video picture        are organized as slices or tiles, a relationship between a        temporal motion vector prediction (TMVP) coding tool and an        alternative TMVP (ATMVP) coding tool, and    -   performing, based on the determining, the conversion;    -   wherein the relationship specifies the applicability as one or        more of the following:    -   (a) in case that the TMVP is not allowed at a slice or a tile or        a picture level, then ATMVP is disabled at the slice or the tile        or the picture level;    -   (b) in case that the TMVP is signaled at the slice or the tile        or the picture level, then ATMVP is signaled at the slice or the        tile or the picture level after the TMVP;    -   (c) the relationship is specified only at a sequence level and        not included at the slice or the tile or the picture level.

10. The method of clause 9, wherein the relationship is signaled in asingle bit in the bitstream representation.

Additional description of clauses 9-10 can be found in the items 3-4listed in Section 4.

11. A method of video coding, comprising:

-   -   determining, for a conversion between a video region and a        bitstream representation, an amount of masking to be applied to        a position of a coordinated of a current block or a current        sub-block of the video region for temporal motion vector        prediction (TMVP) or advanced temporal motion vector prediction        (ATMVP) coding; and    -   performing, by applying the masking based on the amount, the        conversion between the video region and the corresponding        bitstream representation.

12. The method of clause 11, wherein the amount of masking is signaledin the bitstream representation.

13. The method of claims 11-12, wherein the amount of masking is set tono-masking in case that an indication in a signal parameter set of thebitstream representation indicates that motion compression is disabled.

14. The method of any of claims 11-13, wherein the masking is applied bya bit-wise AND operation with an integer MASK whose value is equal to˜(2^(M)−1), where M is an integer, “˜” represents the bitwise complementoperator.

15. The method of any of claims 11-14, wherein the applying the maskingincludes applying the masking resulting in 2K×2K blocks of the videoregion share a same motion information, wherein K and M are differentintegers.

16. The method of any of claims 11-15, wherein M=3 or M=4.

17. The method of any of claims 11-16, wherein M is signaled in thebitstream representation.

Additional description of clauses 11-17 can be found in the items 3-4listed in Section 4.

18. A method of video processing, comprising:

-   -   determining, during a conversion between a current video region        and a bitstream representation, a valid corresponding region for        alternative temporal motion vector prediction (ATMVP) of the        current video region, and    -   performing the conversion based on the valid corresponding        region,    -   wherein the determining is based on one or more of:    -   (a) an adaptive determination based on a characteristic of the        current video region;    -   (b) a basic region having a size M×N pixels, where M and N are        integers;    -   (c) determining a motion vector used for locating the valid        corresponding region, wherein the determining the motion vector        is based on a rule; or    -   (d) determining default motion vectors for the ATMVP coding.

19. The method of clause 18, wherein the current video region is thevalid corresponding region is a function of (a) a width or a height ofthe current video region, or (b) a motion vector compression toolapplied to the current video region.

20. The method of any of claims 18-19, wherein the current video regioncorresponds to a basic region of size M×N that is smaller than a codingtree unit (CTU) region.

21. The method of clause 20, wherein a current video block is inside thebasic region, and wherein the valid corresponding region is a collocatedbasic region.

22. The method of clause 20, wherein a current video block is inside thebasic region, and wherein the valid corresponding region is at leastpartly non-overlapping with a collocated basic region.

23. The method of clause 18, wherein the valid corresponding region isin a different picture than a current picture that includes the currentvideo region.

24. The method of clause 23, wherein the current video region is acurrent video block and a temporal motion vector (TMV) corresponding tothe current video block is (1) set to a default value, or (2) set to amotion vector in a history based motion vector predictor table.

25. The method of clause 23, wherein the determining the default motionvectors for ATMVP coding includes (1) setting the default motion vectorsto a value (0,0), or (2) deriving the default motion vectors from ahistory based motion vector predictor table, or (3) deriving the defaultmotion vectors from a neighboring block.

Additional description of clauses 18-25 can be found in the items 7-10listed in Section 4.

26. A method of video processing, comprising:

-   -   generating a candidate list or motion vectors for a video region        using a rule; and    -   performing a conversion between the video region and a bitstream        representation of the video region using the candidate list,        wherein the rule includes one or more of:    -   (a) rule 1: a candidate corresponding to alternative temporal        motion vector prediction (ATMVP) mode is always considered        during the conversion;    -   (b) rule 2: enablement status of affine mode for the video        region is used in determining availability of zero motion affine        merge candidate in a sub-block merge candidate list for        sub-blocks of the video region;    -   (c) rule 3: using a non-affine padding candidate to a sub-block        merge candidate list for a sub-block of the video region; or    -   (d) rule 4: motion vectors for the video region are derived from        motion vectors of a block covering a corresponding position        accordingto an alternative temporal motion vector predictor        method.

27. The method of clause 26, wherein the video region is a current videoblock and rule 1 further specifies to determine ATMVP default motionvectors by determining a block at a corresponding position that covers acorresponding position of a center point of the current video block.

28. The method of clause 26, wherein rule 2 further specifies to refrainfrom adding the zero motion affine merge candidate into the sub-blockmerge candidate list in case that enablement of affine mode statusindicates that affine mode is turned off for the current video block.

Additional description of clauses 26-28 can be found in the items 11-12listed in Section 4.

29. The method of any of claims 1-28, wherein the conversion includesgenerating the bitstream from the current video block or the currentvideo region.

30. The method of any of claims 1-28, wherein the conversion includesgenerating pixel values of the current video block or the current videoregion from the bitstream representation.

31. The method of any of clauses 1-28, further comprising: determiningthat a temporal block in a collocated picture related with the currentvideo block is coded with CPR mode, and wherein a default motioncandidate is used rather than an ATMVP candidate based on thedetermination that the temporal block is coded with CPR mode.

32. The method of clause 31, whereinthe default motion candidate isindicative of a center position of the current video block.

33. The method of clause 31, wherein the default motion candidate is a(0,0) motion vector, and a reference picture index is equal to zero forboth reference picture lists.

34. The method of any of clauses 1-28, further comprising: determining aposition of the current video block, wherein default motion informationfor use of the ATMVP candidates is based on the determination of theposition of the current video block.

35. The method of clause 34, wherein the position is based on a positionof a sub-block of the current video block.

36. The method of any of clauses 1-28, wherein use of the ATMVPcandidates is based on a flag indicatinguse of the ATMVP candidatesprovidedby a slice, a tile, or a picture header.

37. The method of clause 36, wherein a current picture including thecurrent video block is not an Intra Random Access Point (IRAP) picture,and wherein the current picture is not inserted into RefPicListO with areference index equal to zero.

38. The method of any of clauses 1-28, wherein ATMVP or TMVP is enabledor disabled based on a flag that is inferred to be false for a slice ora tile based on a current picture includingthe currentvideo block beinga reference picture with an index setto M and a reference picture listX.

39. The method of any of clauses 1-28, further comprising: determiningthat a reference picture with an index set to M in a reference picturelist X for the current video block is a current picture, and whereinATMVP is enabled based on the determination that the reference picturewith the index set to M in the reference picture list X for the currentvideo block is the current picture.

40. The method of clause 39, wherein sub-block motion information aredefined to point to the current picture.

41. The method of clause 39, further comprising: determining that asub-block motion information is from a temporal block, wherein thetemporal block is coded with a reference picture pointing to the currentpicture of the temporal block.

42. The method of clause 41, wherein the sub-block motion information isnot scaled.

43. The method of any clauses 1-28, wherein performing the conversionincludes aligning a sub-block merge index for coding.

44. The method of clause 43, wherein a first number of bins are contextcoded, and a second number of bins are bypass coded, the second numberof bins not context coded.

45. The method of clause 43, wherein bins are context coded.

46. A method of video processing, comprising: determining, for a currentvideo block, a motion vector used in an alternative temporal motionvector prediction (ATMVP) process to locate a correspondingblockin adifferent picturefor a conversion between the current video block and acoded representation of the current video block based on aright-shifting rounding process, and performing, based on a result ofthe determining, the conversion between the current video block and thecoded representation of the current video block.

47. The method of clause 46, wherein the right-shifted rounding processis identical to that used for motion vector scaling during theconversion.

48. The method of clause 46, wherein the right-shifted rounding processresults in a rounding to integer value by rounding towards zero.

49. The method of any of clauses 46-48, wherein the motion vector usedin the ATMVP process is used to derive a default motion information.

The following clauses provide some example solutions of techniquesdescribed in items in the previous section (e.g., items 24-29).

50. A method of video processing, comprising determining, for aconversion between a video picture of a video and a coded representationof the video segment using sub-pictures, that a rule of constraintrelated to sub-blocks is satisfied by the conversion; and performing theconversion according to the rule of constraints.

51. The method of clause 50, wherein the rule of constraint specifiesthat a width of a sub-picture S ending at the (j−1) column is set equalto j minus a left-most column of the sub-picture S, due to positions (i,j) and (i, j−1) belonging to different sub-pictures within the videopicture.

52. The method of any of clauses 50-51, whereinthe rule of constraintspecifies that a height of a sub-picture S ending at the(NumSubPicGridRows−1) row is set equal to (NumSubPicGridRows −1) minus atop-most row of the sub-picture S plus one.

53. The method of any of clauses 50-52, whereinthe rule of constraintspecifies that a width of a sub-picture S ending at the (NumSubPicGridColumns−1) column is set equal to (Num SubPicGridColumns−1)minus a left-most column of the sub-picture S plus 1.

54. The method of any of clauses 50-53, whereinthe rule of constraintspecifies that a size of a sub-picture grid in the video picture is aninteger multiple of a coding tree unit size used during the conversion.

55. The method of any of clauses 50-54, whereinthe rule of constraintspecifies that all sub-pictures in the video picture arenon-overlapping, and together cover entirety of the video picture.

The following clauses provide some example solutions of techniquesdescribed in items in the previous section (e.g., items 30-34).

56. A method of video processing, comprising determining, for aconversion between a video unit of a video and a coded representation ofthe video, whether a reference picture resampling (RPR) mode is usedduring the conversion, and performing the conversion based on thedetermining.

57. The method of clause 56, wherein a flag in the coded representationindicates use of the RPR mode.

58. The method of any of clauses 56-57, wherein the RPR mode isindicated at a sequence level or a video parameter set level.

59. The method of any of clauses 56-59, wherein the RPR mode comprisesusing interpolation filters during a motion compensation process toderive a prediction block of a current block of the video unit duringthe conversion based on whether a resolution of a reference picture isdifferent to the current picture, or whether a width and/or a height ofthe reference picture is larger that of the current picture.

60. The method of any of clause 1 to 59, wherein the conversion includesgenerating the coded representation from pixel values of the currentvideo block.

61. The method of any of clauses 1 to 59, wherein the conversionincludes pixels values of the current video block from the codedrepresentation.

62. A video encoder apparatus comprising a processor configured toimplement a method recited in any of clauses 1 to 61.

63. A video decoder apparatus comprising a processor configured toimplement a method recited in any of clauses 1 to 61.

64. A computer readable medium having code stored thereon, the code,when executed by a processor, causing the processor to implement amethod recited in any of clauses 1 to 61.

FIG. 32 is a block diagram showing an example video processing system3200 in which various techniques disclosed herein may be implemented.Various implementations may include some or all of the components of thesystem 3200. The system 3200 may include input 3202 for receiving videocontent. The video content may be received in a raw or uncompressedformat, e.g., 8 or 10 bit multi-component pixel values, or may be in acompressed or encoded format. The input 3202 may represent a networkinterface, a peripheral bus interface, or a storage interface. Examplesof network interface include wired interfaces such as Ethernet, passiveoptical network (PON), etc. and wireless interfaces such as Wi-Fi orcellular interfaces.

The system 3200 may include a coding component 3204 that may implementthe various coding or encoding methods described in the presentdocument. The coding component 3204 may reduce the average bitrate ofvideo from the input 3202 to the output of the coding component 3204 toproduce a coded representation of the video. The coding techniques aretherefore sometimes called video compression or video transcodingtechniques. The output of the coding component 3204 may be eitherstored, or transmitted via a communication connected, as represented bythe component 3206. The stored or communicated bitstream (or coded)representation of the video received at the input 3202 may be used bythe component 3208 for generating pixel values or displayable video thatis sent to a display interface 3210. The process of generatinguser-viewable video from the bitstream representation is sometimescalled video decompression. Furthermore, while certain video processingoperations are referred to as “coding” operations or tools, it will beappreciated that the coding tools or operations are used at an encoderand corresponding decoding tools or operations that reverse the resultsof the coding will be performed by a decoder.

Examples of a peripheral bus interface or a display interface mayinclude universal serial bus (USB) or high definition multimediainterface (HDMI) or Displayport, and so on. Examples of storageinterfaces include SATA (serial advanced technology attachment), PCI,IDE interface, and the like. The techniques described in the presentdocument may be embodied in various electronic devices such as mobilephones, laptops, smartphones or other devices that are capable ofperforming digital data processing and/or video display.

Some embodiments of the disclosed technology are discussed inclause-based format.

Some example embodiments of techniques described in item 22 of section 4include:

A1. A method of visual media processing (e.g., method 3300 depicted inFIG. 33), comprising: determining (3302), for a current video block, amotion vector for use in a sub-block based motion vector prediction(sbTMVP) process to locate a corresponding block in a collocated picturefor a conversion between the current video block and a bitstreamrepresentation ofthe currentvideoblock, whereinthe motion vector used inthe sbTMVP process is computed in accordance with a scaling operation;and performing (3304), based on using the motion vector, the conversionbetween the current video block and the bitstream representation of thevisual media data.

A2. The method of clause Al, wherein the scaling operation comprises atleast one of: a right-shifting operation, a left-shifting operation,and/or a rounding operation applied on the motion vector used in thesbTMVP process.

A3. The method of clause A2, wherein the right-shifted roundingoperation results in a rounding of the motion vector to an integer valueby rounding towards zero.

A4. The method of clause Al, further comprising:

upon determining that a dimension of a collocated picture or a dimensionof a window associated with the collocated picture is different from adimension of a current picture associated with the currentblock or adimension of a window associated with the current picture, applying ascaling operation on the motion vector used in the sbTMVP process.

A5. The method of clause A4, wherein a result of the scaling operationon the motion vector for the use in the sbTMVP process is expressed as:

MVx′=MVx*W1/W2 and MVy′=MVy*H1/H2, wherein MVx, MVy are motion vectorsto locate a block corresponding to the current video block, whereinMVx′, MVy′ are scaled motion vectors of the currentvideoblock, whereinthe dimension ofthe collocated picture or the dimension of the windowassociated with the collocated picture is denoted as W1, H1, and whereinthe dimension of the current picture or the dimension of the windowassociated with the current picture is denoted as W2, H2 respectively.

Some example embodiments of techniques described in item 23 of section 4include:

B1. A method of visual media processing (e.g., method 3400 depicted inFIG. 34), comprising: determining (3402), for a current video block, amotion vector for use in a sub-block based temporal motion vectorprediction (sbTMVP) process to locate a corresponding block in acollocated picture for a conversion between the current video block anda bitstream representation ofthe currentvideoblock, whereinthe motionvector used in the sbTMVP process is computed with respect to a centerpoint of the currentvideoblock; modifying (3406) the center point of thecurrent video block by applying one or more operations; and performing(3408), based on using the center point modified by applying the one ormore operations, the conversion between the current video block and thebitstream representation of the visual media data.

B2. The method of clause B1, wherein the one or more operations includea scaling operation and/or an operation corresponding to addition of anoffset to the center point.

B3. The method of clause B1, further comprising:

upon determining that a dimension of a collocated picture or a dimensionof a window associated with the collocated picture is different from adimension of a current picture associated with the currentblock or adimension of a window associated with the current picture, performingadditional modifications of the center point of the current video block.

B4. The method of clause B3, wherein the additional modifications of thecenter point of the current video block are expressed as:

x0′=(x0−X2)*W1/W2+X1 and y0′=(y0−Y2)*H1/H2+Y1,

wherein the center point of the current video block is (x0, y0), and thecoordinates of the center point of the current video block after theadditional modifications are (x0′, y0′), wherein the dimension of thecollocated picture or the dimension of the window associated with thecollocated picture is denoted as W1, H1, and wherein the dimension ofthe current picture or the dimension of the window associated with thecurrent picture is denoted as W2, H2 respectively, a top-left positionof the window associated with the current picture is denoted as (X2,Y2), and a top-left position of the window associated with thecollocated picture is denoted as (X1, Y1).

B5. The method of clause B3, wherein the additional modifications of thecenter point of the current video block are expressed as:

x0′=(x0−X2)*W1/W2 and y0′=(y0−Y2)*H1/H2,

wherein the center point of the current video block is (x0, y0), and thecoordinates of the center point of the current video block after theadditional modifications are (x0′, y0′), wherein the dimension of thecollocated picture or the dimension of the window associated with thecollocated picture is denoted as W1, H1, a top-left position of thewindow associated with the current picture is denoted as (X2, Y2), andwherein the dimension of the current picture or the dimension of thewindow associated with the current picture is denoted as W2, H2respectively.

Some example embodiments of techniques described in item 24 of section 4include:

C1. A method of visual media processing (e.g., method 3500 depicted inFIG. 35), comprising: determining (3502), for a current video block, amotion vector for use in a sub-block based temporal motion vectorprediction (sbTMVP) process to locate a corresponding block in acollocated picture for a conversion between the current video block anda bitstream representation ofthe current videoblock, whereinthe motionvector used in the sbTMVP process is computed with respect to a point inthe corresponding block in the collocated picture; modifying (3504) thepoint in the corresponding block in the collocated picture by applyingone or more operations; and performing (3506), based on using the pointin the corresponding block in the collocated picture modified byapplying the one or more operations, the conversion between the currentvideo block and the bitstream representation of the visual media data.

C2. The method of clause C1, wherein the one or more operations includea scaling operation and/or an operation corresponding to addition of anoffset to the point in the corresponding block in the collocatedpicture.

C3. The method of clause C1, further comprising:

upon determining that a dimension of a collocated picture or a dimensionof a window associated with the collocated picture is different from adimension of a current picture associated with the current video blockor a dimension of a window associated with the current picture,performing additional modifications of the point in the correspondingblock in the collocated picture.

C4. The method of clause C3, wherein the additional modifications of thepoint in the corresponding block in the collocated picture are expressedas:

x′=(x−X2)*W1/W2+×1 and y′=(y−Y2)*H1/H2+Y1,

wherein the point in the corresponding block in the collocated pictureis (x, y), and the coordinates of the point in the corresponding blockin the collocated picture after the additional modifications are (x′,y′), wherein a width and a height of a window associated with thecurrent picture are denoted as W2 and H2 respectively, a width and aheight of a window associated with the collocated picture are denoted asW1 and H1 respectively, a top-left position of the window associatedwith the current picture is denoted as (X2, Y2), and a top-left positionof the window associated with the collocated picture is denoted as (X1,Y1).

C5. The method of clause C3, wherein the additional modifications of thepoint in the corresponding block in the collocated picture are expressedas:

x′=(x−X2)*W1/W2 and y′=(y−Y2)*H1/H2, wherein the point in thecorresponding block in the collocated picture is (x, y), and thecoordinates of the point in the corresponding block in the collocatedpicture after the additional modifications are (x′, y′), wherein a widthand a height of a window associated with the current picture are denotedas W2 and H2 respectively, a width and a height of a window associatedwith the collocated picture are denoted as W1 and H1 respectively and atop-left position of the window associated with the current picture isdenoted as (X2, Y2).

Some example embodiments of techniques described in item 28 of section 4include:

D1. A method of visual media processing (e.g., method 3600 depicted inFIG. 36), comprising: determining (3602), for a conversion between avideo picture included in visual media data and a bitstreamrepresentation of the visual media data using sub-pictures, that a rulerelated to one or more sub-pictures is satisfied by the conversion; andperforming (3604) the conversion according to the rule of constraint,wherein the rule specifies that a size of a sub-picture in the videopicture is an integer multiple of a coding tree unit size associatedwith the video picture.

D2. The method of clause D1, wherein the rule specifies that thebitstream representation includes a variable corresponding to a width ofthe sub-picture.

D3. The method of clause D1, wherein the rule specifies that thebitstream representation includes a variable corresponding to a heightof the sub-picture.

D4. The method of any one or more of clauses D2-D3, wherein the variablecorresponding to the height of the sub-picture and/or the variablecorresponding to the width of the sub-picture is expressed in units ofluma coding tree unit size.

D5. The method of any one or more of clauses D2 and D4, wherein thevariable corresponding to the width of the sub-picture is equal to adifference between the width of the sub-picture in units of luma codingtree block size and 1.

D6. The method of any one or more of clauses D3 and D4, wherein thevariable correspondingto the height of the sub-picture is equal to adifferencebetweenthe height of the sub-picture in units of luma codingtree unit size and 1.

D7. The method of clause D4, wherein the luma coding tree unit size isdefined as a width or a height of a luma coding tree block array.

D8. The method of clause D4, wherein the luma coding tree unit size fora coding tree unit is defined as a variable CtbSizeY expressed as:

CtbSizeY=(1<<(sps_log 2_ctu_size_minus5+5)), wherein sps_log2_ctu_size_minus5 denotes a size of a syntax element.

D9. The method of clause D8, wherein the variable correspondingto thewidth of the sub-picture is computed as the width of the subpicturewidth multiplied by CtbSizeY.

D10. The method of clause D8, wherein the variable corresponding to theheight of the sub-picture is computed as the height of the subpicturewidth multiplied by CtbSizeY.

D11. The method of clause D1, wherein the rule specifies that a value ofa flag indicates a use of sub-pictures during the conversion.

D12. The method of clause D11, wherein the flag is a Boolean variable.

D13. The method of clause D12, wherein, the use of sub-pictures isindicated when the flag takes a value 1 and a non-use of sub-pictures isindicated when the flag takes a value 0.

Some example embodiments of techniques described in item 29 of section 4include:

E1. A method of video processing (e.g., method 3700 depicted in FIG.37), comprising: determining (3702), for a conversion between a videopicture included in visual media data and a bitstream representation ofthe visual media data using sub-pictures, that a rule related to one ormore sub-pictures is satisfied by the conversion; and performing (3704)the conversion according to the rule of constraint, wherein the rulespecifies that all sub-pictures in the video picture arenon-overlapping, and together the all sub-pictures in the video picturecover entirety of the video picture.

Some example embodiments of techniques described in item 30 of section 4include:

F1. A method of visual media processing (e.g., method 3800 depicted inFIG. 38), comprising: making (3802) a determination, for a conversionbetween a video unit of a visual media and a bitstream representation ofthe visual media data, whether a reference picture resampling (RPR)technique is used during the conversion; and performing (3804) theconversion based on the determination, wherein a flag corresponding tothe determination is included in the bitstream representation at asequence parameter set level.

F2. The method of clause F1, wherein the flag indicates a use of the RPRtechnique, and wherein the flag takes Boolean values.

F3. The method of clauses F2, wherein the flag equal to 1 specifies thatspatial resolutions of coded pictures with respect to the sequenceparameter set are inferred to be changeable, and the flag equal to 0specifies that the spatial resolutions of the coded pictures withrespect to the sequence parameter set are inferred to be unchanged.

F4. The method of clause F2, wherein the flag equal to 1 specifies thatpicture spatial resolution is changeable within a coded layer videosequence that refers to the sequence parameter set, and the flag equalto 0 specifies that the picture spatial resolution does not changewithin a coded layer video sequence that refers to the sequenceparameter set.

F5. The method of any one or more of clauses F1-F4, wherein, whether awindow information of a picture associated with the video unit isincluded in the bitstream representation is irrespective of the RPRtechnique being used or not.

F6. The method of any one or more of clauses F1-F4, wherein a heightand/or a width of the video unit indicated in the picture parameter set(PPS) is inferred to be same as a height and/or a width of the videounit in another picture parameter set (PPS) associated with a samesequence parameter set.

F7. The method of any one or more of clauses F1-F6, wherein thebitstream representation is configured to include a window informationof a picture associated with the video unit irrespective of a value ofthe flag.

F8. The method of any one or more of clauses F1 -F6, wherein thebitstream representation is configured to include a window informationof a picture associated with the video unit, and wherein the flag isindicative of whether the window information is used during theconversion.

F9. The method of any one or more of clauses F1-F4, wherein a heightand/or a width of the video unit indicated in the picture parameter set(PPS) is inferred to be same as a height and/or a width of the videounit in another picture parameter set (PPS) associated with a samesequence parameter set.

F10. The method of any one or more of clauses F1-F4, further comprising:

upon determining that the RPR technique is not used during theconversion, a height and/or a width of the video unit indicated in thepicture parameter set (PPS) is inferred to be a default value of theheight and/or a default value of the width of the video unit s

F11. The method of clause F10, wherein the default value of the heightand/or the default value of the width of the video unit is inferred as amaximum height and/or a maximum width of video units indicated in asequence parameter set (SPS) associated with the video unit.

Some example embodiments of techniques described in item 31 of section 4include:

G1. A method of visual media processing (e.g., method 3900 depicted inFIG. 39), comprising: based on satisfying a condition, selecting (3902)an interpolation filter during a motion compensation process to derive aprediction block of a current block of visual media data, wherein thecondition is based, at least in part, on determining that a resolutionof a reference picture is different from a resolution of the currentpicture and/or that a dimension of a window associated with thereference picture is different from a dimension of a window associatedwith the current picture; and performing (3904) a conversion between thecurrent block of visual media data and a bitstream representation of thecurrent block.

G2. The method of clause G1, further comprising:

upon determining that the resolution of the reference picture isdifferent than the resolution of the current picture or a dimension of awindow associated with the reference picture is different than adimension of a window associated with the current picture, using aninterpolation filter different than another filter used when thereference picture has a same resolution as the current picture.

G3. The method of clause G1, wherein the condition is based ondetermining that W1>a*W2 and/or H1>b*H2, wherein (W1, H1) represents thewidth and height of the reference picture or a window associated withthe reference picture, and (W2, H2) represents the width and height ofthe current picture, or a window associated with the reference picture,and a and b are scaling factors.

G4. The method of clause G3, wherein a=b=1.5.

G5. The method of clause G1, wherein the condition is further based on aheight and/or a width of the current block.

G6. The method of clause G5, wherein the height and/or the width of thecurrent block individually achieves one or more threshold conditions.

G7. The method of clause G5, wherein a mathematical combination of theheight and/or the width of the current block achieves one or morethreshold conditions.

G8. The method of clause G6, wherein achieving the one or more thresholdconditions includes the height and/or the width of the current blockexceeding the one or more threshold conditions.

G9. The method of clause G6, wherein achieving the one or more thresholdconditions includes the height and/or the width of the current blockmissing the one or more threshold conditions.

G10. The method of clause G7, wherein achieving the one or morethreshold conditions includes the mathematical combination of the heightand/or the width of the current block exceeding the one or morethreshold conditions.

G11. The method of clause G7, wherein achieving the one or morethreshold conditions includes the mathematical combination of the heightand/or the width of the current block missing the one or more thresholdconditions.

G12. The method of any one or more of clauses G1-G11, wherein theinterpolation filter selected is applied exclusively on chroma colorcomponents of the current video block.

G13. The method of any one or more of clauses G1-G11, wherein theinterpolation filter selected is applied exclusively on luma colorcomponents of the current video block.

G14. The method of any one or more of clauses G1-G11, wherein theinterpolation filter selected is applied exclusively on a horizontalfiltering direction.

G15. The method of any one or more of clauses G1-G11, wherein theinterpolation filter selected is applied exclusively on a verticalfiltering direction.

G16. The method of any one or more of clauses GI-Gil, wherein a singletap filter is selected as the interpolation filter such that a result ofapplying the interpolation filter is equivalent to copying integersamples.

G17. The method of any one or more of clauses GI-Gil, wherein a 4-tapinterpolation filter or a 6-tap interpolation filter is selected whenthe condition is satisfied.

G18. The method of any one or more of clauses GI-Gil, wherein abi-linear filter is selected as the interpolation filter when thecondition is satisfied.

Some example embodiments of techniques described in item 32 of section 4include:

H1. A method of visual media processing (e.g., method 4000 depicted inFIG. 40), comprising: determining (4002), for a conversion between acurrent block of a visual media data and a bitstream representation ofthe visual media data, that the current block is a combined intra andintra predicted (CIIP) block, wherein an intra prediction block for theCIIP block is generated using a size of a transform unit (TU), wherein,in the combined inter intra prediction (CIIP) block, a final predictionof the current block is based on a weighted sum of an inter predictionof the currentblock and an intra prediction of the currentblock; andperforming (4004) the conversion based on the determining.

H2. The method of clause H1, further comprising:

upon determining that a dimension of a coding unit associated with thecurrent block exceeds a maximum size of a transform unit, splitting thecoding unit into multiple transform units; and

generating intra prediction blocks and inter prediction blocks for eachtransform unit included in the multiple transform units.

H3. The method of clause H2, further comprising:

upon determining that a maximum size of a transform unit is smaller thana threshold value and a dimension of the coding unit associated with thecurrent block exceeds a maximum size of a transform unit, recursivelysplitting the coding unit into multiple transform units; and

generating intra prediction blocks and inter prediction blocks for eachtransform unit included in the multiple transform units.

H4. The method of clause H3, wherein a first intra-predicted block isbased on reconstructed samples of a second intra-predicted block,wherein the first intra-predicted block and the second intra-predictedblock are generated based on splitting the current block.

I1. The method of any one or more of clauses A1 to H4, wherein theconversion includes generating the bitstream representation from thecurrent video block.

12. The method of any one or more of clauses A1 to H4, wherein theconversion includes generating samples of the current video block fromthe bitstream representation.

13. A video encoder apparatus comprising a processor configured toimplement a method recited in any one or more of clauses A1 to H4.

14. A video decoder apparatus comprising a processor configured toimplement a method recited in any one or more of clauses A1 to H4.

15. A computer readable medium having code stored thereon, the code,when executed by a processor, causing the processor to implement amethod recited in any one or more of clauses A1 to H4.

16. A computer readable storage medium that stores a bitstreamrepresentation generated according to a method described in any one ormore of claims A1 to H4.

FIG. 41 is a block diagram that illustrates an example video codingsystem 100 that may utilize the techniques of this disclosure.

As shown in FIG. 41, video coding system 100 may include a source device110 and a destination device 120. Source device 110 generates encodedvideo data which may be referred to as a video encoding device.Destination device 120 may decode the encoded video data generated bysource device 110 which may be referred to as a video decoding device.

Source device 110 may include a video source 112, a video encoder 114,and an input/output (I/O) interface 116.

Video source 112 may include a source such as a video capture device, aninterface to receive video data from a video content provider, and/or acomputer graphics system for generating video data, or a combination ofsuch sources. The video data may comprise one or more pictures. Videoencoder 114 encodes the video data from video source 112 to generate abitstream. The bitstream may include a sequence of bits that form acoded representation of the video data. The bitstream may include codedpictures and associated data. The coded picture is a codedrepresentation of a picture. The associated data may include sequenceparameter sets, picture parameter sets, and other syntax structures. I/Ointerface 116 may include a modulator/demodulator (modem) and/or atransmitter. The encoded video data may be transmitted directly todestination device 120 via I/O interface 116 through network 130 a. Theencoded video data may also be stored onto a storage medium/server 130bfor access by destination device 120.

Destination device 120 may include an I/O interface 126, a video decoder124, and a display device 122.

I/O interface 126 may include a receiver and/or a modem. I/O interface126 may acquire encoded video data from the source device 110 or thestorage medium/server 130 b. Video decoder 124 may decode the encodedvideo data. Display device 122 may display the decoded video data to auser. Display device 122 may be integrated with the destination device120, or may be external to destination device 120 which be configured tointerface with an external display device.

Video encoder 114 and video decoder 124 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard, Versatile Video Coding (VVC) standard and other current and/orfurther standards.

FIG. 42 is a block diagram illustrating an example of video encoder 200,which may be video encoder 114 in the system 100 illustrated in FIG. 41.

Video encoder 200 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 42, video encoder200 includes a plurality of functional components. The techniquesdescribed in this disclosure may be shared among the various componentsof video encoder 200. In some examples, a processor may be configured toperform any or all of the techniques described in this disclosure.

The functional components of video encoder 200 may include a partitionunit 201, a predication unit 202 which may include a mode select unit203, a motion estimation unit 204, a motion compensation unit 205 and anintra prediction unit 206, a residual generation unit 207, a transformunit 208, a quantization unit 209, an inverse quantization unit 210, aninverse transform unit 211, a reconstruction unit 212, a buffer 213, andan entropy encoding unit 214.

In other examples, video encoder 200 may include more, fewer, ordifferent functional components. In an example, predication unit 202 mayinclude an intra block copy (IBC) unit. The IBC unit may performpredication in an IBC mode in which at least one reference picture is apicture where the current video block is located.

Furthermore, some components, such as motion estimation unit 204 andmotion compensation unit 205 may be highly integrated, but arerepresented in the example of FIG. 5 separately for purposes ofexplanation.

Partition unit 201 may partition a picture into one or more videoblocks. Video encoder 200 and video decoder 300 may support variousvideo block sizes.

Mode select unit 203 may select one of the coding modes, intra or inter,e.g., based on error results, and provide the resulting intra- orinter-coded block to a residual generation unit 207 to generate residualblock data and to a reconstruction unit 212 to reconstruct the encodedblock for use as a reference picture. In some example, Mode select unit203 may select a combination of intra and inter predication (CIIP) modein which the predication is based on an inter predication signal and anintra predication signal. Mode select unit 203 may also select aresolution for a motion vector (e.g., a sub-pixel or integer pixelprecision) for the block in the case of inter-predication.

To perform inter prediction on a current video block, motion estimationunit 204 may generate motion information for the current video block bycomparing one or more reference frames from buffer 213 to the currentvideo block. Motion compensation unit 205 may determine a predictedvideo block for the current video block based on the motion informationand decoded samples of pictures from buffer 213 other than the pictureassociated with the current video block.

Motion estimation unit 204 and motion compensation unit 205 may performdifferent operations for a current video block, for example, dependingon whether the current video block is in an I slice, a P slice, or a Bslice.

In some examples, motion estimation unit 204 may perform uni-directionalprediction for the current video block, and motion estimation unit 204may search reference pictures of list 0 or list 1 for a reference videoblock for the current video block. Motion estimation unit 204 may thengenerate a reference index that indicates the reference picture in list0 or list 1 that contains the reference video block and a motion vectorthat indicates a spatial displacement between the current video blockand the reference video block. Motion estimation unit 204 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the current video block. Motioncompensation unit 205 may generate the predicted video block of thecurrent block based on the reference video block indicated by the motioninformation of the current video block.

In other examples, motion estimation unit 204 may perform bi-directionalprediction for the current video block, motion estimation unit 204 maysearch the reference pictures in list 0 for a reference video block forthe current video block and may also search the reference pictures inlist 1 for another reference video block for the current video block.Motion estimation unit 204 may then generate reference indexes thatindicate the reference pictures in list 0 and list 1 containing thereference video blocks and motion vectors that indicate spatialdisplacements between the reference video blocks and the current videoblock. Motion estimation unit 204 may output the reference indexes andthe motion vectors of the currentvideo block as the motion informationof the current video block. Motion compensation unit 205 may generatethe predicted video block ofthe current video blockbased on thereference video blocks indicated by the motion information of thecurrent video block.

In some examples, motion estimation unit 204 may output a full set ofmotion information for decoding processing of a decoder.

In some examples, motion estimation unit 204 may do not output a fullset of motion information for the current video. Rather, motionestimation unit 204 may signal the motion information of the currentvideo block with reference to the motion information of another videoblock. For example, motion estimation unit 204 may determine that themotion information of the current video block is sufficiently similar tothe motion information of a neighboring video block.

In one example, motion estimation unit 204 may indicate, in a syntaxstructure associated with the current video block, a value thatindicates to the video decoder 300 that the current video block has thesame motion information as the another video block.

In another example, motion estimation unit 204 may identify, in a syntaxstructure associated with the current video block, another video blockand a motion vector difference (MVD). The motion vector differenceindicates a difference between the motion vector of the current videoblock and the motion vector of the indicated video block. The videodecoder 300 may use the motion vector of the indicated video block andthe motion vector difference to determine the motion vector of thecurrent video block.

As discussed above, video encoder 200 may predictively signal the motionvector. Two examples of predictive signaling techniques that may beimplemented by video encoder 200 include advanced motion vectorpredication (AMVP) and merge mode signaling.

Intra prediction unit 206 may perform intra prediction on the currentvideo block. When intra prediction unit 206 performs intra prediction onthe current video block, intra prediction unit 206 may generateprediction data for the current video block based on decoded samples ofother video blocks in the same picture. The prediction data for thecurrent video block may include a predicted video block and varioussyntax elements.

Residual generation unit 207 may generate residual data for the currentvideo block by subtracting (e.g., indicated by the minus sign) thepredicted video block(s) of the current video block from the currentvideo block. The residual data of the current video block may includeresidual video blocks that correspond to different sample components ofthe samples in the current video block.

In other examples, there may be no residual data for the current videoblock for the current video block, for example in a skip mode, andresidual generation unit 207 may not perform the subtracting operation.

Transform processing unit 208 may generate one or more transformcoefficient video blocks for the current video block by applying one ormore transforms to a residual video block associated with the currentvideo block.

After transform processing unit 208 generates a transform coefficientvideo block associated with the current video block, quantization unit209 may quantize the transform coefficient video block associated withthe current video block based on one or more quantization parameter (QP)values associated with the current video block.

Inverse quantization unit 210 and inverse transform unit 211 may applyinverse quantization and inverse transforms to the transform coefficientvideo block, respectively, to reconstruct a residual video block fromthe transform coefficient video block. Reconstruction unit 212 may addthe reconstructed residual video block to corresponding samples from oneor more predicted video blocks generated by the predication unit 202 toproduce a reconstructed video block associated with the current blockfor storage in the buffer 213.

After reconstruction unit 212 reconstructs the video block, loopfiltering operation may be performed reduce video blocking artifacts inthe video block.

Entropy encoding unit 214 may receive data from other functionalcomponents of the video encoder 200. When entropy encodingunit 214receives the data, entropy encodingunit 214 may perform one or moreentropy encoding operations to generate entropy encoded data and outputa bitstream that includes the entropy encoded data.

FIG. 43 is a block diagram illustrating an example of video decoder 300which may be video decoder 114 in the system 100 illustrated in FIG. 41.

The video decoder 300 may be configured to perform any or all of thetechniques of this disclosure. In the example of FIG. 43, the videodecoder 300 includes a plurality of functional components. Thetechniques described in this disclosure may be shared among the variouscomponents of the video decoder 300. In some examples, a processor maybe configured to perform any or all of the techniques described in thisdisclosure.

In the example of FIG. 43, video decoder 300 includes an entropydecoding unit 301, a motion compensation unit 302, an intra predictionunit 303, an inverse quantization unit 304, an inverse transformationunit 305, and a reconstruction unit 306 and a buffer 307. Video decoder300 may, in some examples, perform a decoding pass generally reciprocalto the encoding pass described with respect to video encoder 200 (e.g.,FIG. 42).

Entropy decoding unit 301 may retrieve an encoded bitstream. The encodedbitstream may include entropy coded video data (e.g., encoded blocks ofvideo data). Entropy decoding unit 301 may decode the entropy codedvideodata, and from the entropy decoded video data, motion compensationunit302 may determinemotion information including motion vectors, motionvector precision, reference picture list indexes, and other motioninformation. Motion compensation unit 302 may, for example, determinesuch information by performing the AMVP and merge mode.

Motion compensation unit 302 may produce motion compensated blocks,possibly performing interpolation based on interpolation filters.Identifiers for interpolation filters to be used with sub-pixelprecision may be included in the syntax elements.

Motion compensation unit 302 may use interpolation filters as used byvideo encoder 20 during encoding of the video block to calculateinterpolated values for sub-integer pixels of a reference block. Motioncompensation unit 302 may determine the interpolation filters used byvideo encoder 200 according to received syntax information and use theinterpolation filters to produce predictive blocks.

Motion compensation unit 302 may uses some of the syntax information todetermine sizes of blocks used to encode frame(s) and/or slice(s) of theencoded video sequence, partition information that describes how eachmacroblock of a picture of the encoded video sequence is partitioned,modes indicating how each partition is encoded, one or more referenceframes (and reference frame lists) for each inter-encoded block, andother information to decode the encoded video sequence.

Intra prediction unit 303 may use intra prediction modes for examplereceived in the bitstream to form a prediction block from spatiallyadjacent b locks. Inverse quantization unit 303 inverse quantizes, i.e.,de-quantizes, the quantized video block coefficients provided in thebitstream and decoded by entropy decoding unit 301. Inverse transformunit 303 applies an inverse transform.

Reconstruction unit 306 may sum the residual blocks with thecorresponding prediction blocks generated by motion compensation unit202 or intra-prediction unit 303 to form decoded blocks. If desired, adeblocking filter may also be applied to filter the decoded blocks inorder to remove blockiness artifacts. The decodedvideoblocks are thenstored in buffer 307, which provides reference blocks for subsequentmotion compensation.

In the present document, the term “video processing” or “visual mediaprocessing” may refer to video encoding, video decoding, videocompression or video decompression. For example, video compressionalgorithms may be applied during conversion from pixel representation ofa video to a corresponding bitstream representation or vice versa. Thebitstream representation of a current video block may, for example,correspond to bits that are either co-located or spread in differentplaces within the bitstream, as is defined by the syntax. For example, amacroblock may be encoded in terms of transformed and coded errorresidual values and also using bits in headers and other fields in thebitstream. Furthermore, during conversion, a decoder may parse abitstream with the knowledge that some fields may be present, or absent,based on the determination, as is described in the above solutions.Similarly, an encoder may determine that certain syntax fields are orare not to be included and generate the coded representation accordinglyby including or excluding the syntax fields from the codedrepresentation.

The disclosed and other solutions, examples, embodiments, modules andthe functional operations described in this document can be implementedin digital electronic circuitry, or in computer software, firmware, orhardware, including the structures disclosed in this document and theirstructural equivalents, or in combinations of one or more of them. Thedisclosed and other embodiments can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a computer readable medium for executionby, orto control the operation of, data processing apparatus. The computerreadable medium can be a machine-readable storage device, amachine-readable storage substrate, a memory device, a composition ofmatter effecting a machine-readable propagated signal, or a combinationof one or more them. The term “data processing apparatus” encompassesall apparatus, devices, and machines for processing data, including byway of example a programmable processor, a computer, or multipleprocessors or computers. The apparatus can include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them. A propagated signal is anartificially generated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, and it can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for u se in a computingenvironment A computer program does not necessarily correspond to a filein a file system. A program can be stored in a portion of a file thatholds other programs or data (e.g., one or more scripts stored in amarkup language document), in a single file dedicated to the program inquestion, or in multiple coordinated files (e.g., files that store oneor more modules, sub programs, or portions of code). A computer programcan be deployed to be executed on one computer or on multiple computersthat are located at one site or distributed across multiple sites andinterconnected by a communication network.

The processes and logic flows described in this document can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random-access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Computer readable media suitable for storingcomputer program instructions and data include all forms of non-volatilememory, media and memory devices, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto optical disks; and CD ROM and DVD-ROM disks. The processor andthe memory can be supplemented by, or incorporated in, special purposelogic circuitry.

While this patent document includes many specifics, these should not beconstrued as limitations on the scope of any subject matter or of whatmay be claimed, but rather as descriptions of features that may bespecific to particular embodiments of particular techniques. Certainfeatures that are described in this patent document in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable sub combination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a sub combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A method of processing video data, comprising:making a determination, for a conversionbetween a video picture of avideo and a bitstream of the video, whether a first coding tool isallowed during the conversion; and performing the conversion based onthe determination, wherein in the first coding tool, different spatialresolutions are available for different pictures in a video sequence,and wherein upon determining that the first coding tool is not allowedduring the conversion, a height and/or a width of the video pictureindicated in a picture parameter set (PPS) is inferred to be a defaultvalue of the height and/or a default value of the width.
 2. The methodof claim 1, wherein the default value of the height and/or the defaultvalue of the width is indicated in a sequence parameter set (SPS) syntaxelement associated with the video picture.
 3. The method of claim 2,wherein the default value of the height and/or the default value of thewidth is equal to a maximum height and/or a maximum width of the videopicture of the video sequence associated with the video picture.
 4. Themethod of claim 1, wherein a sequence parameter set (SPS) level flag isused to indicate whether the first coding tool is allowed.
 5. The methodof claim 1, wherein the conversion is performed using sub-pictures,wherein a size of a sub-picture in the video picture is in units of acoding tree unit size associated with the video picture.
 6. The methodof claim 5, wherein a syntax element corresponding to a width of thesub-picture and/or a syntax element corresponding to a height of thesub-picture is included in a sequence parameter set (SPS) syntax elementassociated with the video picture.
 7. The method of claim 6, wherein thesyntax element corresponding to the width of the sub-picture and/or thesyntax element corresponding to the height of the sub-picture isexpressed in units of luma coding tree unit size.
 8. The method of claim6, wherein the syntax element corresponding to the width of thesub-picture is equal to a difference between the width of thesub-picture in units of luma coding tree block size and 1, and thesyntax element corresponding to the height of the sub-picture is equalto a difference between the height of the sub-picture in units of lumacoding tree unit size and
 1. 9. The method of claim 1, wherein theconversion includes encoding the video picture into the bitstream. 10.The method of claim 1, wherein the conversion includes decoding thepicture from the bitstream.
 11. An apparatus for processing video datacomprising a processor and a non-transitory memory with instructionsthereon, wherein the instructions upon execution by the processor, causethe processor to: make a determination, for a conversion between a videopicture of a video and a bitstream of the video, whether a first codingtool is allowed during the conversion; and perform the conversion basedon the determination, wherein in the first coding tool, differentspatial resolutions are available for different pictures in a videosequence, and wherein upon determining that the first coding tool is notallowed during the conversion, a height and/or a width of the videopicture indicated in a picture parameter set (PPS) is inferred to be adefault value of the height and/or a default value of the width.
 12. Theapparatus of claim 11, wherein the default value of the height and/orthe default value of the width is indicated in a sequence parameter set(SPS) syntax element associated with the video picture.
 13. Theapparatus of claim 12, wherein the default value of the height and/orthe default value of the width is equal to a maximum height and/or amaximum width of the video picture of the video sequence associated withthe video picture.
 14. The apparatus of claim 11, wherein a sequenceparameter set (SPS) level flag is used to indicate whether the firstcoding tool is allowed.
 15. The apparatus of claim 11, wherein theconversion is performed using sub-pictures, wherein a size of asub-picture in the video picture is in units of a coding tree unit sizeassociated with the video picture.
 16. The apparatus of claim 15,wherein a syntax element corresponding to a width of the sub-pictureand/or a syntax element corresponding to a height of the sub-picture isincluded in a sequence parameter set (SPS) syntax element associatedwith the video picture.
 17. A non-transitory computer-readable storagemedium storing instructions that cause a processor to: make adetermination, for a conversion between a video picture of a video and abitstream of the video, whether a first coding tool is allowed duringthe conversion; and perform the conversion based on the determination,wherein in the first coding tool, different spatial resolutions areavailable for different pictures in a video sequence, and wherein upondetermining that the first coding tool is not allowed during theconversion, a height and/or a width of the video picture indicated in apicture parameter set (PPS) is inferred to be a default value of theheight and/or a default value of the width.
 18. The non-transitorycomputer-readable storage medium of claim 17, wherein the default valueof the height and/or the default value of the width is indicated in asequence parameter set (SPS) syntax element associated with the videopicture.
 19. A non-transitory computer-readable recording medium storinga bitstream of a video which is generated by a method performed by avideo processing apparatus, wherein the method comprises: making adetermination, for a video picture of a video, whether a first codingtool is allowed for generating the bitstream; and generating thebitstream based on the determination, wherein in the first coding tool,different spatial resolutions are available for different pictures in avideo sequence, and wherein upon determining that the first coding toolis not allowed during the conversion, a height and/or a width of thevideo picture indicated in a picture parameter set (PPS) is inferred tobe a default value of the height and/or a default value of the width.20. The non-transitory computer-readable recording medium of claim 19,wherein the default value of the height and/or the default value of thewidth is indicated in a sequence parameter set (SPS) syntax elementassociated with the video picture.